Small playgroup for preschooler with behavior challenges / sensory sensitivity?

My 3.5 year old son has been asked to leave two (very different) preschools due to behavioral challenges (hitting etc.), which crop up almost exclusively in a school-setting or in other groups of more than 2 children. We are now keeping him at home until we can figure out what kind of program would work best for him and what extra therapies/support he may need. He does not seem to be on the spectrum but may have AHDH, anxiety, and/or sensory issues (evaluation in process). Whatever trouble he's having, I believe he could really benefit from regular small doses of social interaction in a very small group setting (<8 kids) guided by a professional. Like a social skills practice group. Does anything like this exist, perhaps something run by an occupational therapist? There were some archived messages about this on BPN but the recommendations seem to be out of date. Ideally looking for something in the El Cerrito/Berkeley area, but would be willing to go further for the right thing. Thanks very much for any advice. Also would welcome meeting up with others in a similar situation for one-on-one playdates. Please feel free to contact me through BPN.