I bought a magazine for a late 1940's Mossberg Model 144 from these people. I would only rate the quality and fit to the gun as a 7/10 but it works. http://www.ammoclip.com/m/mossberg_140_152.htm
The page says " This magazine is also made for:
New Haven models 250C, 250CA, 250CB, 250K and 250KB
$32
No, I haven't cause mine is in good shape, but like I said, it has the tube mag in the stock. Yours has the drop down mag doesn't it?
Mine is a decent shooter. I yours is too. Good luck finding what you need.