RON L here = SERESURPLUS
I've had one of those and it was a fun gun! Magazines for it were always a bear to find and affoard, but if you look in the Shotgun News or use a search engine, type in Gun Parts Corporation or Numurich, they are a good start! They used to carry them as well as the firing pin that was prone to breakage on my M-1 anyhow? If they can't help you, they will turn you on to someone that might?