The PPQ uses the exact same mag as the P99, FYI, so you might have better luck looking for P99 mags.
This is true of the M1, not the M2. P99 mags are identical to PPQ M1. I've read that TP9SA mags work in the PPQ M2. But unlike P99/M1 compatibility, I can't confirm TP9/M2 from personal experience.
I picked up a PPQ yesterday and have owned P99s for some time now, and aside from an orange follower and the floorplate on the PPQ mag saying PPQ I cant see any difference. The P99 mag fits the PPQ and locks back the slide. Both the P99 and PPQ appear to have the same relief cut for the ejector. I havent fired it yet though so the proof would be in the firing. The mag body even says P99 on the PPQ mags.
I have one .40 mag left from a second generation P99 which I sold only because I could not get used to the variable AS trigger pull. It works interchangeably with the magazines I got with my new PPQ.
I ran my P99 mags and SW990 mags through my PPQ today flawlessly. No problems whatsoever.
You can use P99 mags in the PPQ. They just need to be the later version
The early mags I got with my 2001 P99 have significant differences with both the P99 WAF65004(late model P99 mags) and the PPQ mags. Other than the cosmetic differences that spcrobbins mentioned above, the later WAF65004 P99 mags are identical to my PPQ mags and have worked flawlessly in my PPQ. I would not attempt to run the early P99 mags in my PPQ.
There's an earlier version of the P99 that has magazines that are NOT compatible with the PPQ M1, but most P99 mags are. As far as I know, there is no P99 magazine that is compatible with the M2. A couple of pictures:
On the left is an M2, and the two on the right work in the M1. There is only one notch on the M1 style, and it is much closer to the top of the magazine than the two notches on the M2 style.
Looking at the pictures on Bullseye and Northern Republic, they appear to be M1. One notch only, positioned up high.



























