I'd prefer walnut. I can't imagine the K31 being difficult to find. 7.5x55mm isn't something you normally find at the sporting goods store, but if you go to http://www.ammoman.com you can get some specials. On average it can be around $40+ per 20 rounds. Through Ammoman, you can knock that down quite a bit, to prices competitive with more common calibers.

I am a sucker for those style of rifles, having several MN M44's. The K31 is a fine rifle as it can shoot groups so tight you can compete well with scoped rifles.