WHERE CAN I BUY BAKUGAN TOYS

The Bakugan Toys must be the hot item for Christmas.  I have already had a terrible time finding them to buy.  I understand it is some sort of game that involves a Bakugan character that is shaped like a marble you throw on a card to make it open.  Could someone please let me know how this game is played, what specifically I am suppose to look for and where I can buy these toys?