I know that my uncle got a whole lot of them when our state discontinued that design. They didn't mark them, because you had to have the stickers to go on them to make them usable. Also, as I said, the design had changed.
I'm guessing that you want license plates from different states, different years, etc. for atmosphere.
Announcing at church is good (have them check with relatives), and the junkyard idea is great. Also, posting on here was a good idea. I'll check to see if we have anything at home. If we do, I'll get back with you.