I believe the BATFE requires a special additional license and powder magazine for retail sale of (real) black powder, so no one bothers. I think ordering it is going to be the only way to go. I ordered Nul-B Swiss for priming powder a couple years ago, works well.
No way, no how, would Campsite have real black. To meet code, they would need a parking lot the size of the Melville mall. To be fair, black powder can be dangerous. It is almost a gurantee that a black powder factory will blow up. Only question is when.
I particularly like the picture of the barricades used to shield the magazines.