Hi everyone, I just picked up a few 31 round factory mags for my 9mm HK USP-SD pistol. The seller told me that they are beyond rare and I couldn't find any more for sale on the net. Have any of you guys heard about these magazines before and if so how rare are they? I would like to find more of them for sale but have been unable to locate any. Any information about these magazines or where to find more would be great. Thanks...