If you're looking for YuHiO cards, here are a few possible places to buy them online:
Pokeorder carries a wide variety of YuHiO Single Cards, Booster Packs, and Theme Decks.
CrossToy has a more modest collection available, but offers YuHiO booster boxes for sale, which are much cheaper than buying the boosters individually.
Or, check eBay for YuHiO:
YuHiO Video/DVD
Amazon is a good place to find YuHiO videos and DVDs or even books and computer games:
