under a pathway, in the area where あなた and riku ha a 'triathlon' for the privilege of naming the raft, it's in a cave-like place and the entrance is covered によって a rock, I think.
to be もっと見る specific. Mushrooms (Three): One is in a hollow behind a rock, right 次 to Kairi. One is in the bushes on the other side of that same cliff. The last is in the Secret Place, the dark cave on the first side of the island (to the right of the treehouse). A cutscene will play there.
