Here I am! haha I just responded to your other post; unfortunately I'm a little confused as to where you are in the game. But I'll do my best to help!
The key pencil is located in the room to the right of the room where the sword pencil was. You'll need to go down, to the right and then back up to get it then you can use it to activate the drillcart and go back through the sword pencil room!