Dear elizabeth,
I'm late to the conversation here, but also wanted to say welcome! I'm so glad your son is feeling so much better--and I'm sure the friend situation will come with time. I have found it a bit difficult, too (especially as I am very shy myself), but I'm sure you will find that things do improve gradually-- there will surely be some very nice people out there who also want to have lovely chums!
One small idea, that may or may not appeal to you--here we have a homelearners' "hotline"--an email list of activities people are doing, which they invite others to join. If you have something similar where you are, would you feel comfortable posting an activity yourself? I have had the best luck so far just posting something like "we'll be at John Smith park tomorrow at 10; come join us for a walk!", as I find that there are always people looking for informal ways to connect. A lovely child we know loves history, and his mom posted an "old-timers club" recently on the list--and got a bunch of very nice, very interesting children out for the first meeting, where they planned lots of upcoming field trips. Maybe something music-related, since that is one of his passions?
Anyway, welcome, and good luck! It can't hurt that the nicer weather is coming--maybe some beach/park/woods types of outings will be easier to arrange now--
peace
minnie
PS Another place I have sometimes found nice kids is hanging out at the public library during school hours! Any 10 year old out in "public" between 9 and 3 on a school day is probably a homeschooler...