One of the best ways to organize your code in Sails, at least for me and my team, has been to have all the real business logic in Services (/api/services). Those objects can be accessed globally from any controller.
Also, a good practice is working with promises in services (as Sails use them on the model methods)
Just create a Store service (StoreService.js), with your code:
module.exports = {
  findStore: function(storeId) {
    // here you call your models, add object security validation, etc...
    return Store.findOne(storeId);
  }
};
Your Controllers should handle all that is related to requests, calling services, and returning apropriate responses.
For example, in you example, the controller could have this:
module.exports = {
  index: function(req, res) {
    if(req.param('id')) {
      StoreService.findStore(req.param('id'))
        .then(res.ok)
        .catch(res.serverError);
    } else {
      res.badRequest('Missing Store id');
    }
  },
  findStore: function(req, res) {
    if(req.param('id')) {
      StoreService.findStore(req.param('id'))
        .then(res.ok)
        .catch(res.serverError);
    } else {
      res.badRequest('Missing Store id');
    }
  },
};
That way, you have really simple controllers, and all business logic is managed by services.