Check with Jon at Crater Fireworks. His cell number is right on the site, and I found him to be diligent about returning missed calls.
https://www.addictedtoblackpowder.com/back-powder/
I bought black powder from Jon a couple of months ago, after another member here recommended him. Jon had a good selection of Swiss and Schuetzen powders, at that time. His website has been updated since then, and currently shows that he has stock(?).
I was very pleased by his stock, prices, and service. He’s at the top of my list, for next time I start to run low.
That shouldn’t be for quite a while…