Oh, I really feel for you and your son.
My son is also 12 years old and quite lonely. But his domineering spirit and insistence that everything has to be his way is what has caused other kids to not want to be friends with him. He never gets visits or phone calls during the holidays. (Well, he does have one out of town friend, but it doesn't help since this friend is well, out of town). I don't know what advice to give you other than to just be there for your son when he needs to talk. Hug him lots. Tell him you love him.
You sound like a good and protective Mom who only has her child's best interests at heart.
Hopefully some of the other Mom's here can come up with some suggestions.

We often have holiday programs that are independent of schools. I would love for my son to go on one of them as it gives him a chance to make completely new friends. Anything like that in your area?

Hang in there.