Umaril's Sword shares the same model as the Elven claymore.
Two of these blades can be obtained, one from each of two stages in the fight against Umaril. The first can be found next to his bloody corpse (or as loot on his body), and the second will probably have to be caught as the player character and the blade fall from the sky.
Another way to obtain both, as well as a way to make the fight against Umaril extremely easy, would be to use the disarm move, then quickly pick up his sword. He will only be able to cast an occasional spell. This can be done in both the mortal world and the Planes of Oblivion.