Sorry. I have never seen this kind of holster before. Perhaps somebody else on here can help identify.
I think it could be a kriegsmarine pattern... It does exist in brown leather, with KM stamp. As this holster came from the Royan-La Rochelle pocket area in France, it could be the right explanation.
SOLD - Kriegsmarine C96 "Broomhandle" Holster | Legacy Collectibles