Head to Glarials Tomb located NW of the Fishing Guild, you will meet a ghost that will start you on your journey from one ghost to another getting each piece. There is 3 different paths which you may end up doing to get the robes.
Path One
If the ghost says the thief is NE of there:
Your 2nd ghost will be in the Wilderness Bandit Camp.
3rd in the graveyard east of the Wilderness bandits.
The 4th is by the ship for the Dragon Slayer in Port Sarim.
5th ghost is by the alter in the Prayer Guild.
The Final ghost can be found second floor of the Canifis Slayer Tower.
Path Two
If the ghost says the thief is SE of there:
your 2nd ghost is in the Desert Bandit Camp.
3rd ghost is found in the Wilderness Lava Maze by the inner ladder.
The 4th ghost is in the Tree Gnome Stronghold near the Gnomeball Field.
Your 5th ghost would be upstairs of Party Pete's Place.
Final ghost is in the earth warriors chamber under Edgville.
Path Three
If the ghost mentions pirates and shipwrecks:
your 2nd ghost is located in between the Pirates' Hideout and Agility Training Course in the Wilderness.
3rd ghost is by the alter in the Wilderness west of the Lava Maze.
The 4th ghost is on Entrana in the church.
5th ghost is in the Wizard Tower.
Your final ghost is on the second floor of the Rogues Castle in the Wilderness.
