Pennsylvania strictly controls who can ship alcohol into the commonwealth. Some wineries are allowed to ship, most cannot. I’m not aware of any out-of-state distilleries that can ship hard liquor to Pennsylvania residents. I think that is why the in-state distilleries rapidly sold-out of product — there is no viable alternative.
I am sure, given the Commonwealth state’s use of control to restrict it’s resident’s freedom, there are some restrictions on shipments of alcohol from out of state.
However, I know that my brother who lives in PA has his vodka shipped in by the case. I don’t recall where he buys it from though.