I'll be nice - I'm in a good mood since my Form 1 got approved today.
Glocks are on the roster so that LEOs can buy them easily. Glocks were readily available at a time even at places like Bass Pro. Maura wanted Glock to jump through a bunch of hoops to become "MA compliant" and Glock gave Maura the finger. She went after Glock and said "since we can't outlaw them, we'll tell dealers they can't sell them since they won't listen to my demands" hence the "secret list of things you can't buy." The MA approved roster only applies to what dealers can sell and advertise, it doesn't apply to what you can own. By creatively following the letter of the law, dealers discovered they could "sell" Glocks, just as a frame transfer. Not all dealers are willing to do so, but the ones that don't suck cock or operate a deli counter (NES joke) will sell them. Figure out which one you want, and then go find a dealer at the Mill with what you want in stock. Simple as that.