It can be found in the shelves in the building south of the building with the anvils in it in Seers' Village only during the quest; after the quest, a slashed book will be found instead. It can also be found in the bookcase in your house after getting it from Seers' Village. To make elemental shields you need the book or its slashed counterpart in your inventory. After the Elemental Workshop II quest, mind shields can also be smithed.