In NJ, you can purchase 4 oz. of Robitussin AC OTC. That's pretty weak stuff, and if you drink the whole bottle you will have severe diarrhea; they do not want you getting off on this stuff. It's pretty hard to find a pharmacy who will do it (I've only been able to do it at mom-n-pop pharms, and even then they have to know you).

-yawkaw