not a complete answer, but have you considered creating your own scrollbar lookalike:
import tkinter as tk
class MyScrollbar(tk.Canvas):
    def __init__(self, master, *args, **kwargs):
        if 'width' not in kwargs:
            kwargs['width'] = 10
        if 'bd' not in kwargs:
            kwargs['bd'] = 0
        if 'highlightthickness' not in kwargs:
            kwargs['highlightthickness'] = 0
        self.command = kwargs.pop('command')
        
        tk.Canvas.__init__(self, master, *args, **kwargs)
        
        self.elements = {   'button-1':None,
                            'button-2':None,
                            'trough':None,
                            'thumb':None}
        
        self._oldwidth = 0
        self._oldheight = 0
        
        self._sb_start = 0
        self._sb_end = 1
        
        self.bind('<Configure>', self._resize)
        self.tag_bind('button-1', '<Button-1>', self._button_1)
        self.tag_bind('button-2', '<Button-1>', self._button_2)
        self.tag_bind('trough', '<Button-1>', self._trough)
        
        self._track = False
        self.tag_bind('thumb', '<ButtonPress-1>', self._thumb_press)
        self.tag_bind('thumb', '<ButtonRelease-1>', self._thumb_release)
        self.tag_bind('thumb', '<Leave>', self._thumb_release)
        
        self.tag_bind('thumb', '<Motion>', self._thumb_track)
            
    def _sort_kwargs(self, kwargs):
        for key in kwargs:
            if key in ['buttontype', 'buttoncolor', 'troughcolor', 'thumbcolor', 'thumbtype']:
                self._scroll_kwargs[key] = kwargs.pop(key) # add to custom dict and remove from canvas dict
        return kwargs
                
    def _resize(self, event):
        width = self.winfo_width()
        height = self.winfo_height()
#       print("canvas: (%s, %s)" % (width, height))
        if self.elements['button-1']: # exists
            if self._oldwidth != width:
                self.delete(self.elements['button-1'])
                self.elements['button-1'] = None
            else:
                pass
        if not self.elements['button-1']: # create
            self.elements['button-1'] = self.create_oval((0,0,width, width), fill='#006cd9', outline='#006cd9', tag='button-1')
            
            
        if self.elements['button-2']: # exists
            coords = self.coords(self.elements['button-2'])
            if self._oldwidth != width:
                self.delete(self.elements['button-2'])
                self.elements['button-2'] = None
            elif self._oldheight != height:
                self.move(self.elements['button-2'], 0, height-coords[3])
            else:
                pass
        if not self.elements['button-2']: # create
            self.elements['button-2'] = self.create_oval((0,height-width,width, height), fill='#006cd9', outline='#006cd9', tag='button-2')
        
        if self.elements['trough']: # exists
            coords = self.coords(self.elements['trough'])
            if (self._oldwidth != width) or (self._oldheight != height):
                self.delete(self.elements['trough'])
                self.elements['trough'] = None
            else:
                pass
        if not self.elements['trough']: # create
            self.elements['trough'] = self.create_rectangle((0,int(width/2),width, height-int(width/2)), fill='#00468c', outline='#00468c', tag='trough')
        self.set(self._sb_start, self._sb_end) # hacky way to redraw thumb
        self.tag_raise('thumb') # ensure thumb always on top of trough
            
        self._oldwidth = width
        self._oldheight = height
        
    def _button_1(self, event):
        self.command('scroll', -1, 'pages')
        return 'break'
    
    def _button_2(self, event):
        self.command('scroll', 1, 'pages')
        return 'break'
        
    def _trough(self, event):
        width = self.winfo_width()
        height = self.winfo_height()
        
        size = (self._sb_end - self._sb_start) / 1
        
        thumbrange = height - width
        thumbsize = int(thumbrange * size)
        thumboffset = int(thumbrange * self._sb_start) + int(width/2)
        
        thumbpos = int(thumbrange * size / 2) + thumboffset
        if event.y < thumbpos:
            self.command('scroll', -1, 'pages')
        elif event.y > thumbpos:
            self.command('scroll', 1, 'pages')
        return 'break'
    
    def _thumb_press(self, event):
        print("thumb press: (%s, %s)" % (event.x, event.y))
        self._track = True
        
    def _thumb_release(self, event):
        print("thumb release: (%s, %s)" % (event.x, event.y))
        self._track = False
        
    def _thumb_track(self, event):
        if self._track:
#           print("*"*30)
            print("thumb: (%s, %s)" % (event.x, event.y))
            width = self.winfo_width()
            height = self.winfo_height()
        
#           print("window size: (%s, %s)" % (width, height))
        
            size = (self._sb_end - self._sb_start) / 1
#           print('size: %s' % size)
            thumbrange = height - width
#           print('thumbrange: %s' % thumbrange)
            thumbsize = int(thumbrange * size)
#           print('thumbsize: %s' % thumbsize)
            clickrange = thumbrange - thumbsize
#           print('clickrange: %s' % clickrange)
            thumboffset = int(thumbrange * self._sb_start) + int(width/2)
#           print('thumboffset: %s' % thumboffset)
        
            thumbpos = int(thumbrange * size / 2) + thumboffset
        
#           print("mouse point: %s" % event.y)
#           print("thumbpos: %s" % thumbpos)
        
            point = (event.y - (width/2) - (thumbsize/2)) / clickrange
#           point = (event.y - (width / 2)) / (thumbrange - thumbsize)
#           print(event.y - (width/2))
#           print(point)
            if point < 0:
                point = 0
            elif point > 1:
                point = 1
#           print(point)
            self.command('moveto', point)
            return 'break'
        
    def set(self, *args):
        oldsize = (self._sb_end - self._sb_start) / 1
        
        self._sb_start = float(args[0])
        self._sb_end = float(args[1])
        
        size = (self._sb_end - self._sb_start) / 1
        
        width = self.winfo_width()
        height = self.winfo_height()
        
        if oldsize != size:
            self.delete(self.elements['thumb'])
            self.elements['thumb'] = None
        
        thumbrange = height - width
        thumbsize = int(thumbrange * size)
        thumboffset = int(thumbrange * self._sb_start) + int(width/2)
        
        if not self.elements['thumb']: # create
            self.elements['thumb'] = self.create_rectangle((0, thumboffset,width, thumbsize+thumboffset), fill='#4ca6ff', outline='#4ca6ff', tag='thumb')
        else: # move
            coords = self.coords(self.elements['thumb'])
            if (thumboffset != coords[1]):
                self.move(self.elements['thumb'], 0, thumboffset-coords[1])
        return 'break'
        
if __name__ == '__main__':
    root = tk.Tk()
    lb = tk.Listbox(root)
    lb.pack(side='left', fill='both', expand=True)
    for num in range(0,100):
        lb.insert('end', str(num))
        
    sb = MyScrollbar(root, width=50, command=lb.yview)
    sb.pack(side='right', fill='both', expand=True)
    
    lb.configure(yscrollcommand=sb.set)
    root.mainloop()
I've left my comments in, and for the life of me i can't seem to get click and dragging the thumb to work correctly, but its a simple scrollbar with the following features:
- up and down buttons that can be coloured
 
- thumb and trough that can be individually coloured
 
- tracks movement in scrollable widget
 
- thumb resizes with size of scroll area
 
Edit
I've revised the thumb code to fix the click and drag scrolling:
import tkinter as tk
class MyScrollbar(tk.Canvas):
    def __init__(self, master, *args, **kwargs):
        self._scroll_kwargs = { 'command':None,
                                'orient':'vertical',
                                'buttontype':'round',
                                'buttoncolor':'#006cd9',
                                'troughcolor':'#00468c',
                                'thumbtype':'rectangle',
                                'thumbcolor':'#4ca6ff',
                                }
        
        kwargs = self._sort_kwargs(kwargs)
        if self._scroll_kwargs['orient'] == 'vertical':
            if 'width' not in kwargs:
                kwargs['width'] = 10
        elif self._scroll_kwargs['orient'] == 'horizontal':
            if 'height' not in kwargs:
                kwargs['height'] = 10
        else:
            raise ValueError
        if 'bd' not in kwargs:
            kwargs['bd'] = 0
        if 'highlightthickness' not in kwargs:
            kwargs['highlightthickness'] = 0
        
        tk.Canvas.__init__(self, master, *args, **kwargs)
        
        self.elements = {   'button-1':None,
                            'button-2':None,
                            'trough':None,
                            'thumb':None}
        
        self._oldwidth = 0
        self._oldheight = 0
        
        self._sb_start = 0
        self._sb_end = 1
        
        self.bind('<Configure>', self._resize)
        self.tag_bind('button-1', '<Button-1>', self._button_1)
        self.tag_bind('button-2', '<Button-1>', self._button_2)
        self.tag_bind('trough', '<Button-1>', self._trough)
        
        self._track = False
        self.tag_bind('thumb', '<ButtonPress-1>', self._thumb_press)
        self.bind('<ButtonRelease-1>', self._thumb_release)
#       self.bind('<Leave>', self._thumb_release)
        
        self.bind('<Motion>', self._thumb_track)
            
    def _sort_kwargs(self, kwargs):
        to_remove = []
        for key in kwargs:
            if key in [ 'buttontype', 'buttoncolor', 'buttonoutline',
                        'troughcolor', 'troughoutline',
                        'thumbcolor', 'thumbtype', 'thumboutline',
                        'command', 'orient']:
                self._scroll_kwargs[key] = kwargs[key] # add to custom dict
                to_remove.append(key)
                
        for key in to_remove:
            del kwargs[key]
        return kwargs
        
    def _get_colour(self, element):
        if element in self._scroll_kwargs: # if element exists in settings
            return self._scroll_kwargs[element]
        if element.endswith('outline'): # if element is outline and wasn't in settings
            return self._scroll_kwargs[element.replace('outline', 'color')] # fetch default for main element
        
    def _width(self):
        return self.winfo_width() - 2 # return width minus 2 pixes to ensure fit in canvas
        
    def _height(self):
        return self.winfo_height() - 2 # return height minus 2 pixes to ensure fit in canvas
                
    def _resize(self, event):
        width = self._width()
        height = self._height()
        if self.elements['button-1']: # exists
            # delete element if vertical scrollbar and width changed
            # or if horizontal and height changed, signals button needs to change
            if (((self._oldwidth != width) and (self._scroll_kwargs['orient'] == 'vertical')) or
                ((self._oldheight != height) and (self._scroll_kwargs['orient'] == 'horizontal'))):
                self.delete(self.elements['button-1'])
                self.elements['button-1'] = None
        if not self.elements['button-1']: # create
            size = width if (self._scroll_kwargs['orient'] == 'vertical') else height
            rect = (0,0,size, size)
            fill = self._get_colour('buttoncolor')
            outline = self._get_colour('buttonoutline')
            if (self._scroll_kwargs['buttontype'] == 'round'):
                self.elements['button-1'] = self.create_oval(rect, fill=fill, outline=outline, tag='button-1')
            elif (self._scroll_kwargs['buttontype'] == 'square'):
                self.elements['button-1'] = self.create_rectangle(rect, fill=fill, outline=outline, tag='button-1')
            
        if self.elements['button-2']: # exists
            coords = self.coords(self.elements['button-2'])
            # delete element if vertical scrollbar and width changed
            # or if horizontal and height changed, signals button needs to change
            if (((self._oldwidth != width) and (self._scroll_kwargs['orient'] == 'vertical')) or
                ((self._oldheight != height) and (self._scroll_kwargs['orient'] == 'horizontal'))):
                self.delete(self.elements['button-2'])
                self.elements['button-2'] = None
            # if vertical scrollbar and height changed button needs to move
            elif ((self._oldheight != height) and (self._scroll_kwargs['orient'] == 'vertical')):
                self.move(self.elements['button-2'], 0, height-coords[3])
            # if horizontal scrollbar and width changed button needs to move
            elif ((self._oldwidth != width) and (self._scroll_kwargs['orient'] == 'horizontal')):
                self.move(self.elements['button-2'], width-coords[2], 0)
        if not self.elements['button-2']: # create
            if (self._scroll_kwargs['orient'] == 'vertical'):
                rect = (0,height-width,width, height)
            elif (self._scroll_kwargs['orient'] == 'horizontal'):
                rect = (width-height,0,width, height)
            fill = self._get_colour('buttoncolor')
            outline = self._get_colour('buttonoutline')
            if (self._scroll_kwargs['buttontype'] == 'round'):
                self.elements['button-2'] = self.create_oval(rect, fill=fill, outline=outline, tag='button-2')
            elif (self._scroll_kwargs['buttontype'] == 'square'):
                self.elements['button-2'] = self.create_rectangle(rect, fill=fill, outline=outline, tag='button-2')
        
        if self.elements['trough']: # exists
            coords = self.coords(self.elements['trough'])
            # delete element whenever width or height changes
            if (self._oldwidth != width) or (self._oldheight != height):
                self.delete(self.elements['trough'])
                self.elements['trough'] = None
        if not self.elements['trough']: # create
            if (self._scroll_kwargs['orient'] == 'vertical'):
                rect = (0, int(width/2), width, height-int(width/2))
            elif (self._scroll_kwargs['orient'] == 'horizontal'):
                rect = (int(height/2), 0, width-int(height/2), height)
            fill = self._get_colour('troughcolor')
            outline = self._get_colour('troughoutline')
            self.elements['trough'] = self.create_rectangle(rect, fill=fill, outline=outline, tag='trough')
        self.set(self._sb_start, self._sb_end) # hacky way to redraw thumb without moving it
        self.tag_raise('thumb') # ensure thumb always on top of trough
            
        self._oldwidth = width
        self._oldheight = height
        
    def _button_1(self, event):
        command = self._scroll_kwargs['command']
        if command:
            command('scroll', -1, 'pages')
        return 'break'
    
    def _button_2(self, event):
        command = self._scroll_kwargs['command']
        if command:
            command('scroll', 1, 'pages')
        return 'break'
        
    def _trough(self, event):
#       print('trough: (%s, %s)' % (event.x, event.y))
        width = self._width()
        height = self._height()
        
        coords = self.coords(self.elements['trough'])
        
        if (self._scroll_kwargs['orient'] == 'vertical'):
            trough_size = coords[3] - coords[1]
        elif (self._scroll_kwargs['orient'] == 'horizontal'):
            trough_size = coords[2] - coords[0]
#       print('trough size: %s' % trough_size)
        
        size = (self._sb_end - self._sb_start) / 1
        if (self._scroll_kwargs['orient'] == 'vertical'):
            thumbrange = height - width
        elif (self._scroll_kwargs['orient'] == 'horizontal'):
            thumbrange = width - height
        thumbsize = int(thumbrange * size)
        
        if (self._scroll_kwargs['orient'] == 'vertical'):
            thumboffset = int(thumbrange * self._sb_start) + int(width/2)
        elif (self._scroll_kwargs['orient'] == 'horizontal'):
            thumboffset = int(thumbrange * self._sb_start) + int(height/2)
        thumbpos = int(thumbrange * size / 2) + thumboffset
        
        command = self._scroll_kwargs['command']
        if command:
            if (((self._scroll_kwargs['orient'] == 'vertical') and (event.y < thumbpos)) or
                ((self._scroll_kwargs['orient'] == 'horizontal') and (event.x < thumbpos))):
                command('scroll', -1, 'pages')
            elif (((self._scroll_kwargs['orient'] == 'vertical') and (event.y > thumbpos)) or
                ((self._scroll_kwargs['orient'] == 'horizontal') and (event.x > thumbpos))):
                command('scroll', 1, 'pages')
        return 'break'
    
    def _thumb_press(self, event):
        self._track = True
        
    def _thumb_release(self, event):
        self._track = False
            
    def _thumb_track(self, event):
#       print('track')
        if self._track:
            width = self._width()
            height = self._height()
#           print("window size: (%s, %s)" % (width, height))
            
            size = (self._sb_end - self._sb_start) / 1
            
            coords = self.coords(self.elements['trough'])
#           print('trough coords: %s' % coords)
            
            if (self._scroll_kwargs['orient'] == 'vertical'):
                trough_size = coords[3] - coords[1]
                thumbrange = height - width
            elif (self._scroll_kwargs['orient'] == 'horizontal'):
                trough_size = coords[2] - coords[0]
                thumbrange = width - height
#           print('trough size: %s' % trough_size)
                
            thumbsize = int(thumbrange * size)
            
            if (self._scroll_kwargs['orient'] == 'vertical'):
                pos = max(min(trough_size, event.y - coords[1] - (thumbsize/2)), 0)
            elif (self._scroll_kwargs['orient'] == 'horizontal'):
                pos = max(min(trough_size, event.x - coords[0] - (thumbsize/2)), 0)
            
#           print('pos: %s' % pos)
            
            point = pos / trough_size
#           print('point: %s' % point)
            
            command = self._scroll_kwargs['command']
            if command:
                command('moveto', point)
            return 'break'
        
    def set(self, *args):
#       print('set: %s' % str(args))
        oldsize = (self._sb_end - self._sb_start) / 1
        
        self._sb_start = float(args[0])
        self._sb_end = float(args[1])
        
        size = (self._sb_end - self._sb_start) / 1
        
        width = self._width()
        height = self._height()
        
        if oldsize != size:
            self.delete(self.elements['thumb'])
            self.elements['thumb'] = None
        
        if (self._scroll_kwargs['orient'] == 'vertical'):
            thumbrange = height - width
            thumboffset = int(thumbrange * self._sb_start) + int(width/2)
        elif (self._scroll_kwargs['orient'] == 'horizontal'):
            thumbrange = width - height
            thumboffset = int(thumbrange * self._sb_start) + int(height/2)
        thumbsize = int(thumbrange * size)
        
        if not self.elements['thumb']: # create
            if (self._scroll_kwargs['orient'] == 'vertical'):
                rect = (0, thumboffset,width, thumbsize+thumboffset)
            elif (self._scroll_kwargs['orient'] == 'horizontal'):
                rect = (thumboffset, 0, thumbsize+thumboffset, height)
            fill = self._get_colour('thumbcolor')
            outline = self._get_colour('thumboutline')
            if (self._scroll_kwargs['thumbtype'] == 'round'):
                self.elements['thumb'] = self.create_oval(rect, fill=fill, outline=outline, tag='thumb')
            elif (self._scroll_kwargs['thumbtype'] == 'rectangle'):
                self.elements['thumb'] = self.create_rectangle(rect, fill=fill, outline=outline, tag='thumb')
        else: # move
            coords = self.coords(self.elements['thumb'])
            if (self._scroll_kwargs['orient'] == 'vertical'):
                if (thumboffset != coords[1]):
                    self.move(self.elements['thumb'], 0, thumboffset-coords[1])
            elif (self._scroll_kwargs['orient'] == 'horizontal'):
                if (thumboffset != coords[1]):
                    self.move(self.elements['thumb'], thumboffset-coords[0], 0)
        return 'break'
        
if __name__ == '__main__':
    root = tk.Tk()
    root.grid_rowconfigure(1, weight=1)
    root.grid_columnconfigure(1, weight=1)
    
    root.grid_rowconfigure(3, weight=1)
    root.grid_columnconfigure(3, weight=1)
    
    lb = tk.Listbox(root)
    lb.grid(column=1, row=1, sticky="nesw")
    for num in range(0,100):
        lb.insert('end', str(num)*100)
        
    sby1 = MyScrollbar(root, width=50, command=lb.yview)
    sby1.grid(column=2, row=1, sticky="nesw")
    
    sby2 = MyScrollbar(root, width=50, command=lb.yview, buttontype='square', thumbtype='round')
    sby2.grid(column=4, row=1, sticky="nesw")
    
    sbx1 = MyScrollbar(root, height=50, command=lb.xview, orient='horizontal', buttoncolor='red', thumbcolor='orange', troughcolor='green')
    sbx1.grid(column=1, row=2, sticky="nesw")
    
    sbx2 = MyScrollbar(root, height=50, command=lb.xview, orient='horizontal', thumbtype='round')
    sbx2.grid(column=1, row=4, sticky="nesw")
    
    def x_set(*args):
        sbx1.set(*args)
        sbx2.set(*args)
        
    def y_set(*args):
        sby1.set(*args)
        sby2.set(*args)
    
    lb.configure(yscrollcommand=y_set, xscrollcommand=x_set)
    root.mainloop()
so I've fixed the calculation to work out where the new scroll to position will be, and changed from binding on the thumb tag for the track and release events to binding on the whole canvas, so if the user scrolls quickly the binding will still release when the mouse is let go.
I've commented out the binding for when the cursor leaves the canvas so the behavior more closely mimics the existing scroll bar, but can be re enabled if you want it to stop scrolling if the mouse leaves the widget.
As for making two classes, the amended code above lets you use the orient keyword so you can just drop this class (with styling changes) in place of the default scrollbar, as shown in the example at the bottom.