Q:  What do P7 PSP style magazines look like?

A:  P7 PSP style magazines only work in P7 PSP butt magazine release style pistols, and will not work in the P7 M8.  The PSP magazine catches via a cutout at the bottom rear of the magazine.  Here are the PSP magazines:

Q:  Are there PSP magazines available from other sources. 

A:  To the best of my knowledge, there are no aftermarket PSP magazines, but even if there were, the consensus is stick with HK Factory magazines.

There were also some experimental 10 round P7 PSP Magazines made.  Some occasionally pop up for sale on boards frequented by HK enthusiasts.   Here is a picture of some: