The Vandread cards are pretty hard to find, on top of that, there are a bunch of promos. I can't explain my fascination with the show and the cards, but I snap them up when I can.
This website has good coverage of the kind of thing I'm talking about.
There were two trading card sets, one for each season, in addition to a special pack of 6 SP cards. There were also promos released with DVDs and CDs.