Hi Kiwi,
For blank loads in particular, you'll be happier if you can find real black powder. I started searching locally a couple of years ago. I first went to 5 locally owned gun shops and got the same story at each place - for stores, the ATF requires black powder to be stored in a magazine, and there is some additional odious paperwork involved, and they didn't want to mess with it.
No one will have it out in the open - you have to ask.
Digging through old posts on this board I found several people who had found Goex black powder at Bass Pro Shops and maybe some other sporting megastore (Gander Mt.?). I finally hit pay dirt at a nearby Bass Pro Shop. You can buy black powder at several online stores, but hazmat shipping makes it pricy, although it becomes reasonable if you order 5 lbs or so.
andy