"There was once a man who claimed to be the very reincarnation of a fairy. He treasured these tights, and so will you. Kooloo-Limpah! If sold, this rare find can’t be replaced."
As part of the EX Treasure: Fairy Clothes side quest, Link learns from Misko's EX Journal that the treasure is located at at the village ruins next to farmland where many people once gathered. The farmland is the Ranch Ruins, with the Mabe Village Ruins being the runs that are next to it. The piece of armor can be found underneath the inactive Guardian, located at the south end of the Mabe Village Ruins.
Be sure to check our Interactive Map for a more precise location.