I didnt make these, I found these at the lake shore when the water level is low, just start diggin through the cattail roots, theres literally thousands that have collected over the years of hunting, I dont think any native american living or dead would mind me collecting these.
That being said, Id also like to say that I would never desecrate a burial ground or site of that nature just for my indulgance.
The pieces Im finding behind my house are just laying around, right where you said, under an oak tree, as Im blowing leaves they are nicely uncovered without damage, but ya gotta watch for those little guys in the 2nd pic, theres one under every rock!