To be honest the only thing which comes to my mind is Gear Wheels that wears War Golems, Damaged Worker Golems , but it is dropped by other kind of mago-mechanics creatures like Worker Golems, Control Towers, Iron/Golden and Diamond Servants and it's replicas and more.
Of course there is a lot of examples when monster wears an item that can be dropped by other monster, but this item is also avaliable in his own loot.