They sell remnants in large sizes, and even the small sizes will provide enough leather for one holster.
I form fit all my sheaths when the leather is wet and I just use my fingers for it, is easy enough, wet leather is like innertube rubber. You can also use something hard and rounded, like a Zippo lighter or other, just be careful because wet leather marks really easily, your fingernail will leave a permanent mark for instance (trim nails first).
