Regarding a referral service, I would try www.4therapy.com. I b elieve you are correct on insisting he get some serious help, but I am not sure how you should do that. Cutting off money is one lever but it is often seen as punitive, and then creates rebellion. Possibly you could talk to him in such a way as to indicate you want to support him financially to some degree, but not as much as now...a gesture of caring, but would be willing to pay for therapy.
You could get some help preparing for this discussion from the MasteringStress program(link above).
My daughter went through the same as your son. She is now 23, and married. We helped her countless times, bailed her out. She has had just about every job in our area. Averaging 8-10 jobs a year and only working a few months total in a year. Finally we had to step back, and let her do on her own. She didn't starve, she always manage to find a place to stay. As hard as it was, she had to "do" on her own. Today, she has had her job a whole year!! Taking care of business. Yes, she even went to the doctor to seek help on her own. I believe sometimes in order to keep of sanity, parents have to step back and let them fall, and let them learn how to pick themselves back up. I'm from WI and after 17 we couldn't force her to get the help she needed. I don't know about AZ. Good luck to you and your family.