While it may difficult to find there is some kind of nonprofit rehab for him. Few, if any addicts have insurance so don't even worry about that. That eliminates private rehabs but there are public and nonprofit ones. You need to find the rehab place. He has to agree to go. As he's an adult you're pretty much ignored by docs, rehabs and the entire medical system. But he's unlikely to be able to find help himself. So you have to do the legwork.
I have never found the internet rehab locator sites helpful. Here's a couple of other thoughts:
If he goes into the ER for overdose, accident or general medical issue the ER will find him a rehab bed if he agrees to go. But you can call the ER anyway to get a list of rehabs. You'll need to ask for a social worker.
Rehab is considered a psychiatric or psychology service. Call the closest mental health clinic and ask them for a list of rehabs.
Call your local state social services agency. Ask how he would get funding for a rehab, typically Medicaid or state mental health funding. Ask for their criteria for getting him the funding and the procedures... Does he apply for funding or get accepted to the program first? Where is the state rehab program? Typically near a state mental hospital?
None of this is fast or easy. But remember that there is nothing you can do to make him change. This is something that you can do. So the minute he says he wants to go you have a plan in place to take him there and get him in. Have a bag packed for him with all his documents birth cert, ss card, immunization record, doctor name and phone, etc.
I've always found that feeling like I'm doing something productive for him gives me comfort. Having the plan in place, car ready, knowing how to get in the locked detox doors in the middle of the night, ... Knowing I could get him there before his next craving...all comforting. Mind you, at least a few times he'll change his mind before he gets there...or walk out the back door while you"re walking out the front .but this may be the only thing you can do for him.