There are a total of 40 collectible lollipop wrappers in the game for this achievement. Don't confuse these with Lollipop Health pick ups as the collectible ones are golden colored. Some of them can only be found while playing on Hard difficulty and they're usually in plain sight. You can track your progress by pressing start, going to Juliet's Stash, then pressing three times to check your Lollipop Case. They are numbered so you can check to see which one's you are missing.
To find them all please refer to Rep's Lollipop Collectibles & Zombie Album Guide