There's not much out there. If you google ESL developmentally disabled
one of the things that comes up is this post! But try it - there are a few things on the page which look interesting.
I wouldn't normally link to sites outside this one, but given the reason for the request, I hope Eric will forgive me this time
. The site English without Frontiers
provides a course (syllabus, materials, T's notes etc) etc designed for the types of learner you describe. There's a small cost for the paper version or a free online version.