its NOT against the law to buy fireworks in PA.
its against the law for PA residents to buy fireworks in PA.
...its a silly law.
i live in jersey and cannot legally purchase or use fireworks here. however along the NJ/PA boarder, on the pennsylvania side there are fireworks stores. in order to buy fireworks, you have to show ID to not only prove your age, but also to prove that you are not from PA.
so, its legal to sell fireworks in PA, so long as they are not sold to PA residents.
these particular stores on the NJ/PA boarder are unmistakably meant for people who live in or drive through NJ. however when crossing the state line to jersey, your right to even drive with fireworks in your car disappears.
so theoretically these stores should do zero business
:edit: so my suggestion is to find someone who is NOT a resident of PA, and get them to buy fireworks at one of these stores. the ones i know of are along route 80 at the border, though i havent been around there in over 5 years.