HI northjdr,
Several of us here shoot 1 inch bores. Before I give you some advise that might be bad for you, can you tell me a bit more about the barrel? What is the breech diameter (around where the powder would be)?
Any chance of posting a picture?
Pyrodex doesn't work very well for blanks. 2F Black Powder is what you want for blanks in a 1 incher. 1F would be prefered fror live loads.
There are places that you can mail order it, but the hazmat charge makes it expensive per pound for anything less than 5#.
25# is where it gets really cheap. Look at
http://www.powderinc.com for a good place to order black powder. You have to order in 5# increments. The prices include shipping and hazmat charges.
Maybe there is someone else here that knows where you can get some locally.
Rick