I bought a light pattern two years ago, and it came in a very old green baize fabric made plain slip, and it looks great.
It must have been made for it pre war and looks very authentic and wouldn't take much to reproduce.

It just slides into it, and was obviously made for someone to carry to a bell target match or similar in public I would guess, and still comply as being covered up.

I can supply pictures if anyone want to reproduce it.