Are you thinking size/shape or markings?
The reason I ask is that a Glock 22 is essentially a Glock 17 but chambered in .40cal and since there isn't a difference in airsoft chambering so to speak then a Glock 17 will be pretty much the same. A glock 18 also will be the same other than the selector switch on the rear of the slide and the option for full auto.
That all said it should be noted that the vast majority or at least all of the Glocks I've seen in my time in airsoft have been slightly oversized IE the Glock 17 sized guns actually are the size of a Glock 20/21 the 45acp/10mm varients. Doesn't matter much from a general perspective but effects holster fit if your using a fitted holster since it's wider in the slide and frame.
Now further issues, glock has been restricting replicas of their guns for a while now, so finding glocks can be tricky your either buying used. Or your going to risk getting it from overseas and possibly having it caught at the border.
Luke