They're out there but they aren't cheap. Even in only "good" condition, as long as they are complete they command a premium dollar. Some of the later conversions, like the FR7 and FR8 by Spain or the M986 by Brazil are available in 7.62x51 and shoot acceptably. The Russian and other com bloc countries, recently released thousands of Mosin based carbines. The UK and most affiliated countries, gave up issuing carbines in full sized cartridges, 303Brit. Most countries that issued bolt action rifles, issued carbines. There are also other interesting carbines out there, like the Martinis, in 303Brit. In 90% condition, they run well over a thousand dollars. I can rember, turning away from them at $150 and later selling them off, because of the brutal recoil. Oh Well. We can't collect everything and sooner or later channel our gatherings to what inerests us.
The Spanish and Brazilian Mauser carbines are the cheapest and easiest to aquire at this time. If you're not to worried about originality, it's not to difficult to make one up.
One of the reasons these carbines are so tough to find, is that they were usually the first rifles surplussed by their countries. Then, when they hit North American shores in the fifties and sixties, "sporterising" milsurps was the rage. hundreds of thousands of them were cut down or just plain made unshootable. Many ended up in the land fills or on the bottom of local lakes.