Well, I don't play mandolin; but I did some looking around for you, as someone who has spent some time learning to play guitar. Totally different instruments, I know, but I thought it might help me know what to look for.
Here's a link to some useful-looking chord charts:
Free JavaScript Mandolin Chord Chart
And this sight doesn't seem to have very much going on right now, but it has some interesting information about mandolins and mandolin playing in general:
How to Play Mandolin
Hope this helps give you somewhere to start!