Frostreaver can be found in one of the statues in the chapel in the De'Arnise Keep, the statue is guarded by some golems which must be defeated.
|“||This was the axe of Illgarth, a frost giant that terrorized northern communities long ago. It is not known where he acquired the weapon, but he took a perverse pleasure in unleashing it upon small folk, particularly halflings. Ice and acid maimed those not killed, and the giant would laugh coldly if he recognized his handiwork from a previous visit. Ultimately a group did manage to kill him, and at the request of his victims, Frostreaver was buried with him.||”|