I live in Manhattan New York, Harlem to be exact and yes Glocks are used often.. because black market dealers sell them for much cheaper then 600cash.
I've even heard my friend buy one for 225$
I've had people call BS on my claims before, and while it's true that I can't verify them 100%, guns are cheap on the street. I work in a maximum security prison and have plenty of conversations with inmates, half of which are gangbangers. While they lie about plenty of things, some things they don't need to BS about.
One guy (he wasn't a banger) told me he bought a Smith & Wesson 500 XVR for fifty bucks from a friend just a couple months before he came inside. The friend was hard up for money and was jonesing for some smack.
Another guy saw that I had an AK-47 background on my computer screen (we use 'em for database purposed and report writing). He said 'nice gun,' so I asked him if he ever used one. He said he'd fired one a couple times. Of course, he meant full auto.
I was watching "Gangland" on the History Channel one night, and it showed Gangster Disciple members shooting off guns as a New Year's celebration in the (now defunct/bulldozed) Cabrini Green housing project. The next day I asked an older GD who was from Chicago if that really happened. He looked at me like I was retarded and said "Of course. I remember shooting an AK-47 in the air at 3 in the afternoon."
Guns can be had for next to nothing on the street if you've got the right connections. Of course, the type of live you'd have to lead and the company you'd have to keep would far outweigh the costs of legally buying guns at even inflated gunbroker dot com prices. However, if you're a dirtbag and don't mind buying illegal and stolen firearms that were most likely used in homicides and other crimes, you can get them cheap.