There's an unfired SS RSI MkII on GB right now. $1350 to start. Same shop has a couple of ULs (.308 and 7-08) as well. Looks like they're selling a collection.
There's also a .250 built on, of all things, a 1917!
I have a 257R built on a 1909 Argentine Mauser action. If you can find one it should be fine for the 250-3000. I think a small ring Mexican mauser will work as well also.
That was my thought too, have a 22-250 on a Mexican 1936 in the safe that I was planning to re-bore. Yet another project I need to dig out and move along!
Talent is what you're born with, skills are what you earn. - Rod Smith