Caleb KRaft is a great maker, this is a video with examples on how to aid gamers with disabilities.
The Controller Project
This site is a place where you can find documentation on how to modify game controllers for people with physical disabilities. Most of my mods have been used for assistance muscular dystrophy, but the library is an ongoing process and people may find the modifications and accessories helpful for other physical needs.
I will be adding other modifications from around the web as I find them.
If you need a controller modified, or want to share a modification tutorial or 3d printable files, contact me at Hello(at)calebkraft.com