The Justice Center for the Protection of People with Special Needs is a New York state agency. They do many things to support and advocate for people with special needs and disabilities.
Here they provide information on voting rights, accessibility, and other issues for voters who have disabilities.
The American Association of People with Disabilities (AAPD) advocates for increasing the economic and political power of people with disabilities. Their Rev Up! project focuses on increasing voter registration and turnout of people with disabilities, and protecting voters' rights.