Interpol: The Trail of Dr. Chaos

The best thing to do is trying to replay San Francisco (the first level) & try to find 3 white cards in each area. I really advice you to search there because they aren't really hard to find

Play the first mission, San Francisco, and collect 3 cards in each of the three levels. This makes a total of 9 cards.

Take note that each time you play any missions in this game, the Bonus Items (eg, Cards for this solution) will be moved to a different spot on the screen. This is to stop people from memorising their location. Don't be too disgruntled, there is only a handful of locations the cards can spawn so it's still very easy.