Should I find my drunk uncle and tell him to go to rehab?

Tell him to get help.

Find his azz.

Try to at least help him

Maybe ask him if he realises the consequences if he keeps drinking.
If he says yes, then ask him if he would like stop drinking and live longer and suggest help is available.

what if he just needs a drinkin buddy?..

All you can do is let him know. With addicts, they'll never quit until they want to. If your feelings aren't enough to help his desire to want that for himself.. it's not your fault either. & You can't make anyone do anything. But if you don't try, they won't know that they're truly cared about. Knowing that you're loved, helps that decision a lot I think.

Even if they don't realize it now, hopefully someday they might

Naw, at least try. So you wont feel guilty afterwards. Trust me , you dont want that random though in the future