Max Missile Expansion Locations

Grasstown
Right above the building with the motorbike outside/door that needs to be destroyed by a bomb.

Grasstown
Inside the grasstown hut just above the shelter where Kazuma was locked in.

Egg Corridor?
After returning to Egg Corridor. By the sky dragon in where egg 12 used to be.

Egg Corridor?
After returning to the Egg Corridor. Inside the Egg Observation Room?

* Bonus Missile Expansion
Located in the Sacred Grounds secret stage in a chest hidden in a single star block located high on a ledge just before the room with Heavy Press boss fight.