You can see all the different strap types and strap hardware (buckles, tie downs, keepers, clips, etc.) in use on all sorts of stuff swirling around us in daily life. But if you want to get some for your own projects?
Strapworks.com has pretty much all of it. Metal or plastic hardware. All sorts of strap and webbing material.
Inexpensive, easy to work with. Helped me a few times, and I know I will continue to use them when the need arises.