Hey woodchucker, those are about the easiest sheathes to make. It is a folded piece of leather, and the old way of making them only required brass upholstery tacks driven through and bent over to "sew" it together. You could also use a welt, if you like, and rivets or screw posts to fasten it.
No stitching is necessary, no belt loop, just a cut-out in the edge to hold it on your belt or sash. Another style doesn't even have the cutout, just a "wing" at the top of the sheath to hang over the top of your belt.
Make it with a medium-heavy cowhide.
Killdeer