P7M8 magazines are only designed to work in the P7M8 pistols NOT in the PSP style pistols. That is because the P7M8 mags latch with a catch at the top part of the mags, and the mag release is behind the trigger on the frame, whereas the PSP mags latch at the bottom of the rear of the mag via a cutout.
Here are what P7M8 mags look like:
Q: Are there any other P7 M8 magazines available?
A: Yes, ProMag makes P7 M8 magazines, but it is generally regarded that they are not as high quality as factory HK mags, and the consensus is to go with HK Factory Mags.