Massachusetts law requires that all firearms dealers be licensed by the state. In addition, private individuals who sell firearms must comply with several regulations, including background checks on all buyers and completing a firearm transaction form. As such, it is not legal to simply purchase a gun magazine online without going through a licensed dealer. However, there are several ways to buy magazines legally in Massachusetts.
You can find many licensed dealers by searching online or on the yellow pages. You can also check with your local police department to see if they have any recommendations for licensed dealers in your area.
Once you have found a reputable dealer, you will need to complete a firearm transaction form and undergo a background check before you can purchase any gun magazines.