The K-31 rifles are a great buy. Very accurate, slick handling litle carbines. The only slight downside is if you are a cast bulet shooter and want to shoot cast thru them. the throat is pretty shallow. Works fine for jacketed bullets, though.
I've been shooting 7.5 Swiss since Norma was the only game in town. I formed brass from .284 Winchester (just a pass thru a sizing die, no trimming needed in my rifles). Fair amount of Swiss surplus, Swiss match, and sporting ammo available now. Ammunition availablity is much better than it used to be.
Scope mounts are availble now as well, if you want to go that way.