Kynoch in Scotland made sporting ammunition for these for several years. Once in a LONG while, you run into a single round or (if the Stutzer Fairy is watching over you) a whole box.
I have one that left the factory with civilian proofs, although it is a 1917 rifle in full-military trim. Think it must have gone to the police or something; they would be the only ones with enough drag to get a current-issue rifle out of a plant in the middle of losing a war.
I'm forming my ammo from 7.62x54R and it's one of the easiest conversions I've ever done: pick up the MN guys' brass, take it home, lube it, FL size in 7.62x54R dies, open out the case-mouth for a .323 slug, trim to 1.98", load her up.
I don't doubt that there were some of these made as commercials before the Great War (yours is sort-of VERY solid proof of that!) but I really don't think there would have been very many. Add to that the general destruction of firearms during and after a few wars and, my friend, I think you have a VERY rare item.
AND it's beautiful, just to top things off! Straight-pull action, folding Express sights, all the rest. You will need Mannlicher clips for this baby. Do you have such?
Super nice toy!