The few I have found so far: Bright Silver Avenue, there is a poster showing a man holding a paddle saw on the beach. Check to get the Paddle Saw Combo Card. In the food court, where the cook works. There is a poster next to it showing a man holding a bow and arrow. Check to get the Explosive Arrow combo card. In the movie theater, there is a poster next to the bar that depicts an astronaut holding a laser sword. Check to get the laser sword combo card. Also, beat the perverted magician, the one who sawed the woman in half. After killing him, you can get a rocket launcher. Slap the boss Slappy in Everyone Knows Slappy to get a flamethrower combo card. Save the rock hero and get a shock guitar combination card.

I'm exhausted. I hope this helps.