OEM Glock 17 mags are everywhere, what is hard to find is Glock 10/17 OEM Mags. Those list on EE sometimes for near $70 a piece.
If you want the 10/17 SHTF ability with Glock reliability buy KCI mags and spend the difference on an OEM Glock follower, base plate and even springs. It will cost about the same as a normal OEM mag.
For the record though I have plenty of KCI mags, in fact I just got three more in the mail today. While they do have a slightly "cheaper" feel, they work just as fine in my experience. Maybe change the follower if I ever get to it but that's it.