I've just found a UK one, called Release. They don't seem to say that they're anti-prohibition exactly, but they say their working to protect human rights and manage drug use more fairly... whatever that means, they should be clearer really. One of their campaigns is called "Nice People Take Drugs", which I suppose was intended to be a rather incendiary slogan. Personally, I'd prefer to separate entheogenic, positive, harmless drugs from the harmful ones like booze, crack, heroin and meth, and don't think that slogan's going to convince anyone, but it's better than a kick in the teeth (by a policeman).
Check out their deck of cards though, featuring all the politician hypocrites and their confessional quotes! Obama did coke?! :lol:
Release playing cards