There are several websites that supply a US address and credit card purchase facilities My US <-- Link) is one of them.
They will also store items till you have enough of them and then send you them as a single package to save on postage.
I've not used them, but a mate used to have the premium account with that site above, and used them all the time, but he'd opened himself a US bank account and US credit card while he was there, and used that, he only needed the address itself. The site above have quite hefty postage rates, but it may be a better option than having to have US Mates buy things for you and get stuff via them, and there are several other companies offering the same service, and they may have cheaper postage rates. Just google up US address providers. <-- Link)