Brian,
I think what you're doing is pretty cool. Can you please tell me how you're using the cards? Are you teaching math with stats? Are you teaching the kids about collectibles (in general) and how condition could matter? It'd be neat to find out how the cards are being used. I wish I had a teacher that incorporated baseball cards into a lesson plan.
Who knows, maybe some of the guys on the board could come up with different ideas on how you could use the cards as a teaching aid. Since you're looking for 90's cards I would figure you must be teaching a fire fighting course... (you know, set those things a blaze and teach the kids how to put out fires)
It's always nice to see someone that's just trying to make a difference.