The IZh-81 has now been replaced by the MP-133, which appears to be the same design, only with a receiver made to accept up to 3 1/2" shells, and they do make a MP-133K version that feeds from the same sort of box magazine. You may need to write to Izhmech (
http://imzcorp.com/en/info/partners.html ) and see if either the magazines are interchangeable, or if they have any mags for the IZh-81 in stock.