cdnn has the best price for factory magazines. I think I have something like 50+ mags from them and every one is perfect.
http://cdnnsports.com/
They also have a few other selected items. Right now they have HK shooting vests and posters in the odds and ends section. I got one of the vests, and like it. To hot to wear right now but seems well made.
They have an HK knife.
browse though for more stuff.
For a limited time they also have Ranger .40 155g ammo too. You will have to call for that, it's not on the web site.