Pretty sure this is the same as Squires Bingham/Armscor model 20. 10, 15, and 25 shot mags are out there.
Looking closely, my Norinco jw-14 magazine appears similar, but my magazines are polymer. Should be a thread where a fellow CGN'er modded Marlin, or Mossberg to fit too. When I ran a WTB ad for Squires Bingham magazines, I got a couple replies from dealers who had 'em NIP (aprox 45 bucks)
Underrated .22's. Losing the magazine can be a hassle, but be careful to not break the aluminum trigger!