Another "what's the difference between"

Hey again! - I got one of the 500's cleaned and painted today. One of these days I'm going to learn how to post pic's. I know I need to resize........but I'm rambling.
I bought 2 Mopar center caps from ebay this week. They were advertised as "very rare" and "hard to find". Must not have been too rare I was the only one that bid and got them for 6.49. They have the stick in medallion "Limited Edition". Anybody know anything about them, or where I could get two more medallions. They are black with chrome looking lettering. Very cool looking, indeed!
Thanks again - Jim