A good place to begin, here you can search all databases at once. Your results will include books, articles, encyclopedia entries, even videos.
intellectual disability services
mental health services AND impact
Find government information easily by entering site: .gov at the end of your Google search. This should limit all results to government websites.
You can narrow the number of results you get by searching databases individually. In addition to the ones suggested below, try searching other databases on the MCC Library's List of Databases A-Z.