http://www.safariland.com/products/h...ting-holsters/
Maybe one of these would be suitable, readily available, and not terribly expensive to try out. As a general purpose field holster, I heard good things about the molded nylon Bianchi products.
I think, for myself, that I'd like to use crossdraw for a heavy-ish revolver, and would lean toward the 111 Cyclone. Looks to be available for the 3" Ruger GP series.