Long gone are the days when the average USA citizen could purchase black powder at their LGS. Fed regulations on BP storage, along with added red tape and taxation and limited demand for the holy black have see that happen. I get my Swiss BP via mail order, but if the current gun control panacea continues, methinks that mail order BP may end as well, and that will force those who who require that powder (cartridge as well as muzzleloader) to consider making their own, particularly if a flintlock is the weapon to feed. Notice I didn't say "bootleg their own".
I've yet to make black powder, but I have acquired the necessary ingredients and will commence that task shortly.
IF done in a "proper safe manner" - and there IS such a method - the results will almost always not yield a powder equal to that of the commercial Swiss or Goex, but it is still better than nothing and at least will allow my flintlocks to function as they should. Current SAFE black powder making processes appear to be 20-25% less "powerful" than the commercial variety and upping a charge by that percentage closes that gap significantly, so I'm told by more than a few prominent sources. The three black powder making ingredients are readily available to anyone from multiple sources, both online and local to each of us. The tools and materials to effect the BP making process are elementary.
"Safe" BP manufacture means never mixing all three ingredients together DRY, always WET.
Let's put things in perspective. Just as with loading a muzzleloader or making metallic cartridges, there is a safety risk that we all are forced to negotiate. Wet powder of any ilk means safe powder. Wet black powder will not ignite let alone burn. That horn of 2F Goex you've got dangling at yer side is about as close to walking around with a pipe bomb or grenade as it can get. Is that not safe?
For decades there have been EXTENSIVE threads on the CastBoolits forum on making black powder. Several of those threads are posted on even today. The matter of the legality of making any gunpowder ends with each of us, with or without local, state, and federal laws.
Without powder, firearms won't work, and their inclusion in a firearms website/forum is almost a given ... or should be.