the later generation mags are metal.........inside. If you do a search you'll find the terms NFML, FML. The earlier generation mags did not have a metal liner inside, all the newer ones do. Do an E-bay search for Glock mags and also gunbroker.com, you'll find plenty of factory Glock mags for sale.
If I messed up on the mag descriptions pleas someone correct me, thanks