There are 3 stories in the game and each story contains 4 levels. Each individual level contains 3 Chameleons for a total of 12 per story and 36 throughout the course of the game. They show up on-screen while completing the courses and are slightly faded but the majority of them are easily spotted.
If you are having trouble, a guide to all their locations can be found HERE. It is important to note that you have to complete the level to save your progress. Don't just grab an item and quit out or the item you picked up will NOT register.