A dwarven longsword forged from an obscure silvered alloy.
These swords, for two were found, are of dwarven make. Their design is not fancy, being simple and functional. What makes them special is their alloy, forged by a long-forgotten process. The alloy mixes silver with steel in a manner that holds a keen edge, but damages creatures normally immune to steel weapons. Lycanthropes, some undead, and many creatures from distant planes share this vulnerability.
These two swords were carried by goblins who set upon our heroes while they camped. The hunters were actually seeking the werebear, but attacked the camp when they discovered it. Our heroes defeated them, and claimed the swords from the bodies.