Try leatherworker.net. It's a forum that can provide all sorts of info on leatherwork. I used to subscribe to a magazine entitled, "The Leathercrafters and Saddlers Journal". Every month they had an instructional article including patterns for various things, including cowboy and horse tack and accessories. I have to tell you, though, that with the price of leather and the quantities you are forced to purchase, and the price of leatherworking tools, it's cheaper to buy the articles already made, unless you plan to make more than one or two, and unless you want or need a high level of customization. Then again, there are folks like me who just like to buy tools and make their own stuff...to heck with the cost.
@Saddlebag: I plan to graduate to saddles soon, myself. Whose course did you take?