I think QuicKutz has a lego die cut that is pretty cute. And I got some lego brads from the eyelet outlet at a convention (not sure if they sell online).
And YEARS ago, I found some solid colored cardstock that was embossed with the flat Lego type circles. Maybe you could do a search for Lego papers.
Good luck! Sounds like a lot of fun. My kids love legos. Me, not so much; I'm always stepping on them! LOL~
Try this site for the Lego papers and embellishements.
http://www.mousememories.com/Legolan...enter_364.aspx