I know this is probably laughable but I purchased an HK 9mm from a friend a few months back and can't remember the exact model. I'm looking for simple accessories and not sure what's interchangeable with what or even where to look for them. The pistol was purchased from www.hkspecialist.com if that helps. Anything I should know or buy in regards to this? I've attached a couple pics. Thanks in advance for the help.