Arn, who has that Chinese elm-stocked rifle, also makes furniture out of cottonwood, in the Populus family. Big logs and crotches can have some fantastic grain and be quite hard. Don't know how it would be for a full stock, but you could get half-stocks. I bought an old under-lever 12 gauge French shotgun (forget the make) from a farmer in North Dakota. There was no forend, just the lever to turn to the side to open the action, but the buttstock was chopped out of a piece of cottonwood with an axe, and looked like it too!