essbee,
First thing I would ask is whether your DS has a Statement or not. No statement to my mind equals no support.
Have you contacted the NAS? (National Autistic Society).
Also have you looked at IPSEA's website; there's a lot of info on there re permanent exclusion. www.ipsea.org.uk
What have the LEA said to you about this matter?.
Sorry for all the questions but answers to the above may help you further.
I would also post this on the Special Needs board; you'll get more responses on there (it seems more widley read that this particular board) to your question along with more suggestions as to what to do.
Am sorry this is happening to you, the self same scenario happened to a friend of mine and her son is now in a special school (at that time he was supported by a Statement). It was very badly handled by the school in question.