Looted from Pelinal Whitestrake at the Barrier Tower of Agea.
After Pelinal Whitestrake has been defeated, his cuirass can be crafted at an Anvil of Zenithar using the following materials:
Pelinal Whitestrake at the Barrier Tower of Agea
Pelinal Whitestrake is one of the most famed characters in Elder Scrolls lore, known for being a savage warrior. He aided the Alessian Empire in wiping out the Ayleids, including slaying their champion Umaril. His story is the main focus of the plot of the 'Knights of the Nine' DLC expansion.