Most sporter versions of the US Krag are just shortened rifles or altered carbines, perhaps with some extensive stock work, but with issue barrels. 

There are other versions with slightly altered actions, usually a modification to allow slightly longer cartridges to feed through the magazine.  I have seen these in .35 WCF and .405 WCF.  These have completely new barrels and usually new stocks. 

Probably the most common non-30/40 version was rebarreling to .25/35 Winchester.  The Krag action fed the 25/35 case with no alterations necessary.  Since the 25/35 works in the action, the other bottleneck cartridges based on the same case (30/30, etc) should also feed well.  These can be found with either new stocks or just worked-over military stocks.  These conversions were made because many hunters considered the 30/40 cartridge to be excessively powerful.

Krag actions were also used to make .219 Zipper, .22 Hornet & variants, .22 Savage HP, and .25 Krag varmint rifles.  All those are usually found as single shots, and usually with new stocks.