The costume shop is found in Biala Mountain.
Whilst stocking a wide variety of costumes, you will have to be fast to buy one. Like, speed-of-light fast. On entering the shop you will most likely come across this message in place of the stock:
|'We have sold out of all of our Costumes! We will restock with more items soon.
Why not search for your item in user shops using the Shop Search?'
Many poor Maradans are too slow and unlucky to stumble across any form of stock in here. However, some more... dishonest maradans will take advantages of 'Ticker timers' to get their hands on the costumes as soon as it restocks. Tsk tsk. How do you sleep at night, cheaters.