"The AccessText Network helps college students with print disabilities by connecting their disability service offices directly with leading textbook publishers to obtain electronic files. These files are used to create accessible versions of the textbooks."
I've been using their new Accessible Textbook Finder, which allows you to search NOT ONLY their collection, but also Bookshare, Learning Ally, etc. It's great!
And here's a secret! You can use their search tool even without being a member! You can be looking for a book for a k-12 student, it doesn't matter-- this tool just helps you search all sources.
TIP- the ISBN search field only accepts up to 13 numbers, so get rid of dashes before cutting and pasting an ISBN nunber into the search. And if the ISBN number doesn't show up, search by title.