first you must buy the troopers from the toy store.after that they appear in several locations in woodys roundup. There are 5- if facing the front of town hall is north 1 is east, 1 is directly behind you on top of the saloon, over where slink is 1 is at the highest point you can reach, you would have been there once before to throw a cow down, the fourth one is on the opposite end of the map from the dam - can only be accessed once you get the breaking the dam mission, and number 5 is directly in front of the entrance to the bandit lair
each gives you one obvious landing point but make sure you look around using the left stick to spot others. there are a six at each one. you use the left stick to move once thrown and the right is to look around to adjust your view. this helps when making sure the shadow is over the taget so you can hit b and drop on it for the win. a couple of the less obvious ones can be seen if you are looking around while diving
remember that once you are close to the ground it becomes much harder to turn.