As far as taking the test goes, at least in my state, they do offer accommodations for those with disabilities, so if you needed to be in a room by yourself, or low lighting or something simple like that I'm sure they could help you out. Something bigger, like more time to finish the test, is another matter and you'd have to talk with them about it.
I haven't heard of prep courses specifically for autistic or other learning disabilities, but it's worth asking. If they don't have anything, the local autism society might.
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