Debs, I wonder if the National Association for Gifted Children could help, since your ds is bright? The sub is quite expensive, but they may do concessions (if you need one), and they have one-to-one support schemes as well as local groups. They're accustomed to bright children being seen as disruptive/difficult, and tend to go for behavioural responses rather than drugs, eg Ritalin. They have a helpline, too, staffed by helpful people.
Also, this may be asking for the moon, but I'll suggest it anyway. Is there any way you could get a student in to sit with ds while he works, and help/encourage him? We got an Italian student to tutor ds in exchange for speaking English to him, which was a fantastic one-off deal, but you might be able to think of something along those lines, especially if you have an English language school nearby. It would mean he could get used to working quietly with another adult.
Also, in my opinion, there's a great deal to be said for schools programmes on TV, or educational videos from the library - I swear my ds learnt a huge amount from them, even if he was sitting watching TV for longer than most parents would like. My dd is 7 and likes watching them when she's off sick - she then comes and tells me fascinating facts she's learnt off the telly, as if to justify her staying off school
It sounds like you're going through a difficult time, I hope things sort themselves out.