All you can do is get on your phone and call all the gun stores/sports stores in your area. Dont be surprised if some of them mix "real black" up with pyrodex, or worse yet dont know what it is.
In order for a store to sell black powder, they have to have a "magazine" so big, and so many feet from they're store, to store it in, which you will find none of them have.
I order most of my black powder from "Grafs". It is no hassle, if you order at least 5 pounds. you can mix the granulation also. This is what I would do.
Good luck Dave.