I don't know what your capability is as far as paying for treatment. There is a great place in Texas called Menninger Clinic that offers several different programs for people who are dual diagnosis and also programs for those who are not. They have a young adult program referred to as Compass that your son sounds like he might fit right in to... it's geared toward 18-30 year olds making the transition from adolescence to adulthood. It's a really expensive program but I have heard great things about it. Hope you find something.

http://www.menningerclinic.com/p-compass/index.htm