Don't bother trying to rechamber the Krag. I don't know about your area, but in the Pacific NW, Krag brass still shows up at the gun shows, though I will admit not much lately.
I've got a few hundred virgin cases (mostly R-P) that I haven't gotten to use yet, so I'm not really in the market right now. All were bought at gun shows over the last few years.
I'm a bit unusual, my .30-40 Krag is a Ruger! (No.3)
and my Krag is a Norwegian in 6.5x55mm Swede!
There were Krag rifles (outside the US) made in other calibers, the only one still "alive" is the 6.5x55, and don't even think of trying to convert a .30-40 to that.
If you find a mad machinist, who wants a real project, it might be possible, but for sure it will cost you more than the price of two or three good modern rifles. I wouldn't bother.
Just buy .30-40 when you can find it, and when you do find it, stock up a bit.
I got mine!
(and no, not interested in selling any
)
Good Luck!
oh, and when you get into handloading, DO NOT try to maximize the Krag, its a good way to destroy the rifle and maybe get hurt. They are old, the metal alloy isn't as good as modern steels, heat treatment was done "by eye" and they only have ONE locking lug. Stick to 2200fps for 180gr and 2000ish fps for 220gr (or less) and be happy with it. Those loads have killed dead everything that walks in North America, including record size grizzly bear, so don't worry about being undergunned. Do your part, and the Krag will do it's part, every bit as well as it has been doing since 1898.