Sheath/scabbard/holster templates?

[ThisIsMyFirstRodeo]

Perhaps I’m wrong, but most hobbyists don’t seem to need to make more than a handful of sheaths. 
While I don’t by any means specialize in sheaths or scabbards, I tend to stick in that groove. 
But, my beginner’s luck has started petering out, and I find myself needing to up my game in design/construction (as opposed to patterning/decorating, but I need to up that as well…). 
So what titles are the gold standards of sheath making, and what are other unicorns that you’ve found? TIA

[DieselTech]

I think Al Stohlman has some books on knife sheaths & pistol holsters & scabbard. 

Slickbald has a bunch of different patterns. 

On the knife sheaths I just get the knife from the owner & make a pattern from poster board in design they want. 

6 shooter/cowboy revolvers I just use the gun again to make a pattern from poster board.