There is also this organisation
http://www.pspeur.org/
I don't know about the support group you mentioned, but sometimes it helps to talk to people that know about the illness but also been in your position. Its very important that you also get support.
I understand what you mean about the right time. Even if it isn't now it wouldn't harm to look around at local homes to see what is out there for him. Again you can talk to his social worker about it.
I presume he is under a Consultant. Have you talked to them about his treatment and prognosis? Is his medication needing to be reviewed?
Do you get any respite care at the moment. If you don't you should?