On this page of our guide to Psychonauts 2, you will find Supply Chest Keys available in The Motherlobe.
There are 6 Supply Chest Keys in this level.
This key can be found after you're locked in the room by your new classmates. Go to the back end of the room, look left and you'll spot the key on top of the pipes. You can easily reach it with a double jump.
Milla's Room. To reach this key you need to jump on top of a wooden shelf on the left side of the room.
To get to this key, you need to jump on a wooden rack located on the left side of the room.
You'll find the key under the stairs. All you have to do is destroy the cardboard boxes standing in your way.
This key is hidden behind the fan. You have to stop it with your special power.
Location: Nerve Center.
You'll find this key on a wooden shelf on the left side of a large room.