Not sure if you ended up finding something, but there are music therapy professionals out there. You could try Play Your Part in Mission Viejo.

Perhaps try contacting CSU Northridge's music therapy department? I realize that isn't in Orange County, but the staff may have some good resources for you. Music therapy has been so helpful with our kid- we've been working with students at ASU for about two years now. Totally worth it.

https://www.autismspeaks.org/resource-guide/by-...
Have you tried the Provider Directory.
Maybe put up a post at the local college..