One of the first things that popped into my mind was the effect of closure on domestic display fireworks manufacturers. Maybe they get their black powder from China. Another issue is BP for use in artillery propellant charges. Civil War and Revolutionary War battle reinactors also may have a tough time.
Yes, if you are into muzzle loaders, you can make your own black powder, the main item needed is Potassium Nitrate. If anyone has a copy of the military manual called "Improvised Munitions Handbook" (TM 31-210), a method for making BP is given. It also gives instructions on extracting Potassium Nitrate from natural sources. Regardless, no home made BP will come close to the quality of the commercial product. Incidentally, duPont was so successful in selling his BP because he was responsible for making many advances in BP manufacture in France. When he fled from the French Reign of Terror to the USA, he brought all of those BP manufacturing secrets with him, and duplicated the French powder plants in Delaware. His product was much better than any of the other domestic powder makers.
"screen it or press it into pucks too break down later to get almost 20# of black powder for a little over $60."
That operation is the one which is most dangerous and nearly always is responsible for fires and explosions in industrial BP manufacture, especially breaking up cakes into granules.