Unfortunately, I am unsure the answer to your question. Though I too had difficulty with my education because of Dysautonomia. My parents ultimately decided on allowing me to continue my education over the Internet.
Similar to the college courses often advertised on television, there are accredited Internet grade schools for younger students. Examples include: Laurel Springs, Eagle Christian, Compuhigh, etc.
I'm sorry I cannot be of more help. Perhaps another member of our community will have more insight to offer.
The first thing that comes to mind is http://www.dynakids.org/ . . . I'm uncertain how much advice or help they can give but I would try connecting with parents there.
Secondly, realize that the laws protecting your son's rights are very strong and that a good attorney should be able to help you resolve this, so you are moving in the right direction.
Have you tried your local congressmen/women or your local senate person?
They have an education department in each state where different ones handle different things.
You can look them up on your govt website and put together a short 1 page letter kind of like your post and ask what can I do about this problem or where do I turn?
Not only that - look up your state's department of education home front; head of of all schools, send the same letter or fax them.
I had to do this with our youngest son who is Autistic when I needed help. It really gets some wheels rolling; but make sure you're seeking their advice "asking" them for help or where to turn for a specific problem.
Is the lawyer for you or the school district? If it's for the district I wouldn't talk to anyone from there. I found out - the district do not want to be bothered by parents and complaints or problems so they often defer back to the principal's decision at the school level.
If it's a lawyer for your side, make sure you take any and every piece of documentation you can think of or contact you've had with the school or district.