Turns out there's a Tandy Leather Store a few miles north of me.
For sixteen bucks I got a very thick 1-inch wide rawhide strip about 40 inches long, a bottle of black leather dye, and four very substantial steel buckles. They also have brass buckles.

I already own a leather punch for different sizes holes, so I now have the raw materials for about 10 more straps. The leather is really thick.... 'way thicker than any of the other stuff I've used.

http://www.tandyleather.com/

Looks like they have an online store, too.