The American Horticultural Therapy Association, http://www.ahta.org, can help identify a nearby horticultural therapist who is adept at working with people with disabilities in gardens. The association also provides referrals to local healthcare agencies and public gardens with horticultural therapy programs, educational opportunities, and publications.
The Chicago Botanic Garden's Horticultural Therapy Services program (http://www.chicagobotanic.org/therapy) is widely known as a resource for people with disabilities who are interested in gardening. The program manages a demonstration enabling garden staffed by experts with a wide variety of accessible garden features and an extensive adaptive tool collection that visitors can try out among more than 600 different types of plants. The program also offers publications, including the "Garden for Life" series of fact sheets about barrier-free gardening and educational programs that encourage safe, comfortable lifelong gardening.
Use Internet search engines with the key words: enabling garden, healing garden, accessible garden, horticultural therapy, and barrier-free gardening, etc., to identify links to many different resources related to gardening for people with disabilities.