I haven't seen such a study. However, I know for a fact that quite a few guns were floating around after WWII. But these were mainly M98's, and Luger pistols. I'm sure other weapons were also out there. Every now and then a newspaper article pops up with someone finding an old gun or grenade hidden (intentionally) inside some wall or something by some long deceased person. But at least here in Norway, I don't think the number of weapons from that period are high. And probably just a drop in the ocean compared to all the illegal weapons smuggled in by criminals.

Erik