So sorry to hear you reached out to NAMI and his doctor with no success. Sadly this happens a lot.
Of course, you could simply go to NAMI family meetings for supprt but you need help now.
If it was me, I would try his psychiatrist office again and ask to speak to a RN if he has one...or if associated with a clinic, a RN or the office manager, to voice my concerns and lack of communication from his doctor.
Yes, do continue to get a referral from another physician for medication management. Would his PCP be of any help in hooking you up to a new psychiatrist? If you explain your situation to your son's primary care physician he/she "might" be able to do something.
I have been in your shoes. And I have always found if I ran into walls, I would speak to the RN in charge/supervisor or office manager in charge. I would by-pass the doctor and reach out to supervisors, etc.
They don't want to hear complaints...and perhaps I am bias but I always feel a supervising/in charge RN can get results.
Hang in there..."try" not to stress. I know - so easy to say.