As Kael said, it's very rare. When the game was first released, there was a miscoding that allowed it to be won in the slots (your Mark that you had already was counted as a card in the deck, or something like that), and a few people did. It was quickly fixed, but now people are able to win them from Tournaments, and if they happen to have the Mark in their decks when you play against them in the Top 50, there's a VERY small chance you'll win the card.