Leather and wood are materials that can work well together much like iron or other metals and wood.
In case anybody has any interest here is a page with information on various thickness measuring systems. In my work for many years I used the "iron" system just because it was common back in those days.
https://www.libertyleathergoods.com/leather-thickness-weight/
If you need leather Goodwill is your friend as Ed said. So are yard / garage sales. I keep an eye out for belts, high shaft boots and purses for leather. You can also make friends with your local shoe repairman. I used to have craft people drop in to ask for scraps. Much like the big box I keep by my table saw for cut-offs I kept a box for leather scraps and another for rubber scraps.
I try to get in a little target shooting with a few muzzle loaders (nothing fancy) and in black powder shooting one common item is what is often called a "possibles bag" (you can google that). I have a few and recently I was at a yard sale where I picked up an appropriate looking ladies leather purse that I bought for that use. All I need to do is add to its rustic look, probably by adding a strip of leather fringe to the bottom of it.
.
