Individuals with intellectual disabilities (ID, formerly mental retardation) benefit from the same teaching strategies used to teach people with other learning challenges. This includes learning disabilities, attention deficit/hyperactivity disorder, and autism.
Have you tried consulting the people you want to teach? You could contact any of the organisations that support people with learning difficulties/disabilities in.
Teaching Manual Signs to Adults With Mental Retardation Using . extended Osborne and Gatch's () study to hearing impaired, mentally disabled adults.