You can't. I think you used to get them in the magazines (the UK ones). But you can still buy some of the trading cards on eBay.
you can buy Toontown game cards in Walgreen's or probably in game stop
Rite Aid, CVS, Best Buy :)
you can buy club penguin trading cards at your local newsagents
Do not get the trading cards get kinz style or the figures the codes are junk
You are able to buy the most recent New Moon trading cards at the Amazon website.
You can buy Moshi monsters trading cards A.K.A Mashup cards at a Spar Shop or if you buy a Moshi Mag sometimes they have some cards free with the issue. Hope this helped Add me on moshimonsters:cairnrodgers
Almost any place like Wal-mart. And there is a new store called Alco, I think u can buy them from there. They also have the cards on the website so that u can buy them online. And go 2 ebay, they will have some tht u can buy for a few bucks :)
You can buy Trading Card Binders at the Wshop:)
Specific shops sell Trading Cards.
Poundland
eBay
you can buy it from news angents