There are only two kinds of mags, heel release for the P7s and the PSPs and side release for the P7-M8s. Of course the P7-M13 and P7-M10 use their own mags (although many use the P7-M10 mags in the P7-M13 when the ban was on and one could not buy P7-M13 mags, so like with the USP and USPC people used the 10 round 40 mags in the 9mms). The P7 has the heel mag release flush with the grip while the PSP has the narrower heel mag release that extends past the grip, but they use the same mag, only the release on the pistol is different.
Mags can usually be gotten from CDNN and Midway USA had them a couple of weeks ago.
Also, HKparts.net may have some.
For more reading check out the World of HK on HKPRO and also this site
for info specific to the P7s and M4s.
There is a lot of confusion about what is a PSP. An actual PSP is very rare and has the narrow mag release that extends past the grip and will have "PSP" engraved on the left side of the slide as you will see when you check out the P7 pages above. The rest are P7 pistols and most people, including HK when they import and ship them, call them PSP but they actually are not PSPs. There have been some of these P7s come in with the narrow and mag release that extends past the grip and some even have PSP engraved in block letters on the slide, but I am not certain these are real PSP pistols since they usually come in with the P7s. The PSPs that bring the big bucks are the ones with PSP engraved on the slide but do not say P7 on the grip and has the PSP markings like those shown on the above P7 link. IMO those are the real PSPs, not the ones coming in now with the little block letters saying PSP and then P7 on the grip.
The pistol you bought is the standard run of the mill P7, heel mag release that does not extend past the grip, no heat shield, flat firing pin bushing. You will need a tool to remove the firing pin bushing but if you want, you can replace the flush firing pin bushing that needs a tool for removal to the P7-M8 rounded type that one does not need a tool to remove. Midway USA sells them for about $70 which is a lot of money just to remove the firing pin bushing easier. CDNN sells the P7 FPB tool for about $10 if your pistol does not have one and Midway often has the cylinder scraper and brush.