Realize the rifle cal is marked as to "Bore" diameter, which is most likely not the nominal size the round would have been named & sold under. Most likely a cartridge from the 11-11.15mm group. There were some straight cased rounds as well as botleneck versions of this nominal size (including the Mauser round) so without further info as to case type & dimensions would be impossible to tell if brass is available or formable from easily procured existing ones. Some are, some may not be.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra