I was sad to learn of Ken Yankelevitz's death earlier this year (31st of August 2016). Ken was very likely the first person to build and sell accessible controllers in mainstream gaming magazines and he did it at a loss so that controllers were affordable. Atari would recommend people to him directly if in need of alternative controllers in the early 80s at a time when Atari was the biggest video gaming company on the planet.
Ken's family put together a folder including some testimonies from the many people he helped along the way, which I'm told brought him and his family great comfort and happiness. Learn a little more about Ken's work here and here.