Via [Rockpapershotgun]:
For years the AbleGamers Foundation has been advocating for more accessible games as well as supplying specialized hardware such as mouth-operated joysticks and eye trackers to play games for those who have difficulty with traditional controllers. They've recently created the Player Panels initiative to help connect developers and researchers to people with disabilities as accessibility testers, applicants will be compensated for their time though the initiative may be limited only to those living in the USA.

Their site and application form is [here].