There are 4 in total; one in levels 2, 3, 6, and 8.
Level 2: Just do the two things where you stop on the pad(the activities) then go back to the starting point and there it is. This is the beginning, right in front of you, get the blue thing, then go inside the pipe right ahead of you and get that one. Next go back to the start point and get the blue thing there. Once you get this one it unlocks the Time Challenge. Not sure if you actually have to get the Time Challenge complete or not but as soon as I completed the Time Challenge which you have to find 4 of those blue things and went back to the beginning, standing in front of the pipe, it was on my left.
Level 3: After you open the garage door by throwing cubes into the bucket pay careful attention to every corner you turn in the building. The case is in an easily missed corner in there.
Level 6: It's floating on a satellite directly behind you once you start the trash collecting mission
Level 8: About half way through the level there will be a large Red Zone. On the left and right side are raised platforms with Stewards on them. The left one holds this item. The right one holds the Special Object 8.