http://www.copagcards.com/wpt-and-wsop
Copag makes the cards for these branded tournament series. Note at the bottom states that these cards are not for sale. Typically, these cards are not for sale to avoid them getting mixed in to these branded events (given you have them in your backpack while attending) and only post tourney/used ones would be for sale. Used ones normally will have a corner shaved off to mark the deck.
So you will need to Amazon or E-Bay available used decks or maybe the Rio Gift Shop might sell them. But the chances of coming across a new deck of the official cards would be nearly impossible. Bicycle has wsop cards but the logo is different and the card itself is a different material.