While I'm not in a position to donate a controller, I am happy to help you troubleshoot.
The stick mechanism used on the main stick is the same as the C-stick. With most controllers, you'll be able to replace the two mechanisms with a simple screwdriver (the really old models will require some soldering).
Note you'll need a tri-winged screwdriver to open up the controller.
Flip the controller over, there are two screws n the underside oyou'll need to remove which are holding the stickbox in place (they're just the standard four-winged ones).
Now remove the thumb caps, you'll find two black mechanisms holding the stickbox in place. You can un-snap the black bits by pulling away (they're still to be stuck to the motherboard but just not clamped down after you do this). Do this for both sticks and you'll be able to transplant the C-stick to the main stick. Because it's used less, it should give a tighter feeling.
Try this at your own risk, however. I've done it quite a few times and there are a few guides on Youtube as well in case I was not descriptive enough.
What's wrong with your triggers?
