Model 42M(c) was made 1947-1950.
1944-1950
Your rifle is a Mossberg Model 42M, made between 1940 and 1950.
Depending on condition, from $100-200.
Assuming you mean a Mossberg Model 42M(b), between $75 and $200, depending on condition. These are excellent target rifles.
Go here: <http://www.havlinsales.com/> Click on .22 parts & scroll down 1/4 of the page for MOSSBERG .22 SCOPE MOUNT For models 26B, 26C, 42A, 42B, 42C, 42M, 43, 44US, 46A, 46B and 46M.
42m equals -966 = -924
This is a previous trademark used on Montgomery Ward Rifles and Shotguns. Most of these models were manufactured both domestic and international through subcontracts. this model is a knock off of the Mossberg 42M mfg. between 1940-1944. It does not have the "good" wood or the trapdoor buttplate for the extra magazine.
It can be simplified to -41m
42m
90
You can usually find spare magazines at gun shows, where i got mine, but maybe you can order spares from mossberg directly.... Oh and The hole in the rear of the buut stock is actually a storage compartment for a spare magazine, but on some models it's drilled somewhat smaller, so the magazine has to be inserted into it bottom first, otherwise the bottom of the magazine can become caught on the hinge.