I was given my FIL's Stevens 410 for my son to shoot tree rats with. The only problem is there is no magazine with it. The barrel is marked Model 58 A B, 2 1/2 and 3 inch shells. the magazine release is closer to the trigger guard and towards the muzzle there is a small lip proud of the stock and a large slotted screw. What style magazine do I need and where do I need to shop for it? Thanks from a 13 year old wanting to get into the woods.