Thirty-round polymer magazines can be bought from Amazon.com and MidwayUSA as of August 2015. MidwayUSA sells items that are specifically for guns, while Amazon.com offers a more broad range of items to choose from besides the polymer magazines.
MidwayUSA has an inventory full of items for shooting, ammunition, hunting or gunsmithing. Although the site has a lot of 30-round polymer magazines to choose from, Amazon.com may be considered a more reliable source to buy from. The site features a lot of reviews that shoppers can read to be sure that the items they are interested in purchasing are the correct choices for their needs.