Below is a list of all the ●BUBBLER● ammo you can find during the game. The ●BUBBLER● itself will be picked up when opening any of these chests.
Pipeworks S. Reach the end of the map, then turn around and try walking into the bottom of the ledge. Continue through the pipe to the left to reach this chest.
Grasstown Tower. After defeating Suto for the first time, return to the second floor of the tower. Nurse Hasumi will have brought the chest up from the basement for you.
Eroding Valve. Return here after receiving the ●BOOSTER v0.8● from Booster, and fly up to the left to reach this chest.
Labyrinth S, Save Room. After completing the first part of the Labyrinth maze, you'll be in the upper left area of Labyrinth S. Head to the lower right of this area to find a Save Room, and open the chest to the right to find the BUBBLER itself.
Labyrinth C. At about the middle of the area, head to the left to come to a pair of moving blocks. Wait for one of them to hit the wall, then jump or fall past it to get by unscathed. You'll find this chest in the small room afterward.
Aqueducts. After entering the area from the Teleporter Room, head to the right to find a small puzzle revolving around streams of water. Jump past the first redirect, stay still at the second, then jump and fly up with your booster for the third. You'll be spat out next to this chest.
Outer Wall. To the right of the Egg 00 door, fall off the edge and fly underneath it. Carefully head to the left to reach this chest.