Howdy--You're rifle is certainly interesting, and in beautiful condition. I don't know anything about your cartridges, but you may be able to buy new ammo for your rifle through Quality Cartridge in Hollywood, Maryland. If you google the name the web page will come right up. According to the Mannlicher Collectors Association this outfit does a fine job with the original proprietary rounds, and it may well be able to load for your gun as well. The list of obsolete and obscure chamberings offered on the web site is pretty amazing. Good luck with your rifle, and let us know how it shoots!
Malcolm