My daughter has dabbled in the horse world since she was a teen in 4-H. She has boarded her horses at friends who show world champions in various shows. She helps train their horses and then shows them herself occasionally. It is too rich a hobby for her to ever get fully emersed in it.
However, being that she mingles (LOL) in that world she has access to leather workers who are top notch. It takes a lot of hard work to get to that top notch place, but once you are there your saddles, other horse gear, leather people gear will get you to a place where you can make BIG money with your work!
You can also go to local(county) and state horse shows, and things like hat bands, key fobs, boots, holsters, any type of horse/rider gear//decorations will bring you a nice price. Leather journal covers seem to be in demand...decorated with a horse theme, or personalized with horse carving and horses name. These local shows are more a craft like atmosphere.
Those are some of the things I have seen at her horse shows.
Good luck with it.