How does I make these chairs?

Red Round Chair = Gach-only. I'm sure someone will be able to tell you which one exactly.

Seal Chair = Pink and Blue are received as a prize (one only, based on your gender I believe) from a quest. Once you have a Hectagon Necklace in your inventory, a quest from Arwen the Fairy of Ellinia will appear. To complete the quest, you have to give her the Necklace and one each of every REAL eraser (Octo, Lupin, Wraith, Slime, Mushmom and Stump).

Other Seal Chairs (Gold, Black, w/e there is) = Gach-only.

lol @ Greg

Not by gender, you have a 50% chance at getting blue and 50% chance of getting the pink.