Dan, I get all my leathercrafty supplies and tools from online suppliers, the closest Tandy store is 3 hours away (yeah, I live out in the sticks...). If Tandy doesn’t have what I’m looking for, Weaver Leathercraft usually does...but they are not the only places. It pays to shop around, as everyone has sales going on all the time.
As far as buckle placement goes, I usually set mine up so the buckle is on the front. I have heard of folks who prefer it in the back, to keep it from chafing on their rifle or other gear...just a matter of preference, I guess.
Another great source for inspiration is Pinterest...just search for shooting bags, muzzleloading accoutrements, etc.
Enjoy!
Greg