Talk:Collectable Stat Cards/@comment-3357420-20120616001613/@comment-3069692-20120616052156

You can not buy them, the 6th card in each series is a reward for getting the other 5. When you have all cards in a series is opens up a loot drop chance. When you finally get that item in a loot drop it gives you the corresponding card in the reward series. Get all 5 cards in the reward series and you get the 6th card / bonus item.

I think that is the way it works, i don't collect them myself.