All of the above, and also collectors who realize how nice it would be to have a genuine pistol belt, ammo pouch, canteen, etc. from the same era as their weapon. The problem is this stuff is pretty ephemeral compared to the weapons themselves. It was easier and cheaper to find M1956 and M1967 gear in the middle 1970s than it is now. Hence a lot of unmarked repros, and repros with fraudulent markings.
Some items, like carbine-related canvas, were made in such huge numbers that genuine un-issued items were still available at decent prices until a few years ago. To correctly finish my Stevens trenchgun, I spent $20 for a genuine WW2-still-in-the-wrapper web sling, when it would probably have cost $1 ten years ago.
One source, with waaaay too much to absorb at one time, is olive-drab.com. I notice a lot of European interest in this stuff. Probably because they can't have the weapons, but would like some genuine accessories to go with their state-approved non-guns.
I saw these two products for $30 today.
1. Summitsoft "Systemtech XP". Lots of features including registry cleanup (which i believe it needs).
2. Migo "Registry Repair". Mostly registry cleanup, and a couple other items.
Any recommendations?