Candy Sugar Kingdom

You can obtain it from Level 5 and Level 10 Bosses. Both can drop the Rainbow Pearl. If I still remember correctly. :3

Ps: You can get the Rainbow quest from NPC Teddy.

For the quest OMG Not Again (Attained from Zack), the right sock is received after defeating the monsters in the level 7 area. This area is located under the super mushroom room, and it has a house in the center. This area has pink jellies and red mushrooms. This quest is after the super-mushroom quest. I took half a day to get the sock. Advised to proceed with a party as many enemies needed to be defeated to get the sock.

For "Where's My Cookie," cookies can be found at level 9 bunnies.

for the blueberry pie quest, you get blueberries with purple jellies btw