Here are some sites of friends and colleagues in the industry that you might find interesting.
Pyrotechnics Guild International
This is the worldwide organization of firework professionals and amateurs. One of the main attractions to joining the PGI is the annual convention held somewhere in the United States attracting most of the 3,500+ members!
Burt sells mortars for shooting display fireworks and also builds racks.
These are the guys to go to if you are looking for a show in or around the Oil City/Franklin Pennsylvania area!
Crackerjacks Fireworks Club
One of the oldest regional clubs in the US. They have club events in PA, VA and MD.
P.O.R.C - Pennsylvania Organization of Recreational Chaos