The first two bosses are located in Jaga Moraine, Avarr the Fallen is in the top left corner up a hill following a path of enemy bone minions and Whiteout is close by to the east up a circular hill surounded by Avalanches and Ice Elementals. You will find the Fragment of Antiquities in the very north-west corner of the Sepulchre of Dragrimmar, Level 1, in Drakkar Lake. Be sure to obtain the actual quest The Anvil of Dragrimmar for the dungeon as well, from Outrunner Remlok just outside it, or you won't be able to proceed past the first room.