There are a few places that sell kits. Most of those include things like the anvil for setting snaps, which you may or may not need. The sheath for the curved carving knife is the first time I’ve used a snap, so those tools sat unused for a couple years.
The other thing to do is to keep an eye out for used leather goods. A neighbor sold some chaps (for protecting your legs on a motorcycle) very cheaply a couple years ago, and had I been thinking, I could’ve bought and reused those for quite a few projects.