If you can't reasonably tell who's Pmags you found, then there's no misappropriation of lost property.
Find 4 Pmags on Elm and Oak on the sidewalk. You look around and see no one, no one is looking for them. You put an ad in the paper, "found some personal property on the sidewalk at Oak and Elm. Please contact to describe the property and date of loss and I will return it to you."
Then I'd say, you covered it pretty well.
On the other hand, I feel nervous even about "rebuild kits." Even an eventual acquittal in a higher court is a lot of suffering that I don't want any part of.