Friends

I have a 9 year old son with high functioning autism. He is in a small speech & language class, and has friends, but nobody seems to want to socialise outside of school hours. My son is desperate to have friends over for tea etc, but I have almost given up hope of this ever happening. What else can I do to find a friend for my son to meet up with on a regular basis during school holidays, weekends etc? He is extremely lonely and I fear for his future if he is going to suffer this lonliness indefinitely.