The README says you'll need gettext and Lua. You should be able to install those using MacPorts (gettext and lua ports). Then you'll need to modify the system.mk file to point to the installed Lua and perhaps other stuff. It will be trial and error and you'll need to read every error carefully. For example, I get this error when I run make right now:
…
In file included from output.c:23:
private.h:15:21: error: libintl.h: No such file or directory
…
make[1]: *** [output.o] Error 1
However, the file exists:
$ locate libintl.h
/opt/local/include/libintl.h
/opt/local/var/macports/software/gettext/0.18.1.1_2/opt/local/include/libintl.h
Another option is to look at an older Portfile and follow the build process yourself, but note that it's for an older version of ion3. Best of luck!