Vikktorya
Okay so I bought a formula that needs cherub feathers and imp potion. I know cheesy but I wanted to start with something.
Cherub Feathers can be found in the Philosopher's Cache: Garnet. So can 23 other items, but it's not a RIG; though you can only take one item from each Cache, you get to choose the item. The Garnet Cache is a random draw from the basic Philosopher's Cache, which you can buy for 50k in the Bifrost or a whole lot less than that in the MP; also, you can get both basic and colored Caches from Dumpster Dive fairly often.
Angel Imp Potions are on sale at the gold shop Skin Tyte. They are also granted by the Aquarium Overseer from time to time.