Where can I find the materials needed to make a bomb?

I just beat Balrog for the second time, rescuing the robot he so callously crushed. And, good news! He'll build a bomb for me so I can free the voice trapped in the closet!

He wants Charcoal, a Gum Base, and a Jelly Jar - I know how to get the Jelly Jar, but the Charcoal and the Gum Base elude me.

I did find a door with the word "Gum" written on it, but the door is locked, so I'm unsure how to get through if that is where to go.

I have no idea on the charcoal.

Where can I find these items?

(I'm playing Cave Story+, if that matters)

• The Jellyfish Juice is obtained from the Big Jelly that appears after talking to Chaco.

• The Charcoal is obtained from Santa's house (at the start of the zone; you retrieved his keys for him). Use the Jellyfish Juice on his fireplace. Yes, you'll have to get it again.

• The Gum Base is obtained in the locked building on the rightmost part of the level; the trapped Kazuma will give you the Gum Key after defeating the robot, with which you can unlock the door.