Unlikely that you can buy loaded ammo, but if it does turn out to be the likely round that C. mentions above it should be relatively easy to load for. Rim and head dimensions of the 11,15x65R "LK" are the same as the easily available 9,3x74R round according to Dixon's "European Sporting Cartridges vol 1" and cast bullets are available in lots of weights in diameters between .430" and .446" these days, whatever this one turns out to measure.
Chamber cast and bore slug will tell the tale.
The pictures on gunbroker show a broken upper tang just under the thumb piece of the top lever barrel selector. My guess is that the stock has at one time been broken right through the wrist.
