Create A Race That Finds All Collectibles:

Enter the race editor. Press Start to go into the layout mode (overhead view). Press L1, L2, L3, R1, R3, and X. The game will create a race with a checkpoint on up to 30 collectibles you don't already have. Test the race to collect them all. Some will still be hard to collect. Delete the checkpoints once you're done and do it again to find any remaining collectibles.