TripleK manufactures a replacement, though I don't if anyone is importing.
These are nifty rifles, barrel n' receiver are one piece. Worth your while trying to find a magazine for sure. Magazines pop up from time to time on gunbroker, n' fleabay.
I would also consider trying to modify a different magazine to work with it. New Mossberg(702) n' Marlin(70/795) magazines both are slim profile, straight bodied, and cheap enough to experiment on.



























