If you or your son has not tried it, I suggest looking at Neurofeedback. The system I am familiar with is Neuroptimal, which is one-size-fits-all, non directive dynamical neurofeedback that simply acts as a mirror and allows the brain to track itself, become aware of itself, and thereby gradually adjust itself. I got this for a child in foster care that I was the CASA for, and it was incredibly helpful. Her anxiety remitted entirely. She is thriving, over a year later.
Is there a way of gathering a support group, in a web based format like Skype, for kids who share these experiences?