| Claxon |
Or you could simply look in the NPC Codex on the PRD under the barbarian entry and find the appropriate level barbarian.
Edit: Nevermind this wont actually work because they're constructs. Constructs are immune to mind affecting effects including morale bonus that are provided by rage.
I'm not sure if classic treasures revisted accounts for that, but I'm guessing it doesn't. This item now doesn't really work as well as it should because of the change in rage and how it functions. Better to say that the horn temporarily summons dead humanoids from Valhala to fight. Makes more sense mechanically.