I agree that that is a great idea, my guess is that others have tried to do it but have not succeeded, because it is a daunting task!
When our team goes to regional competitions, I take pictures of all the other robots the first day, and put them on our web page that night. I doubt this happesn at every regional event though, and I haven't tried to coordinate my efforts with those of other people.
First place I'd look would be
http://www.thebluealliance.net/