The rae mob Bannok Grimaxe drops the plans for the arcanite ripper which sell for an average of 18K gold on the ah.
He can be farmed very efficiently by using the command /tar bannok grimaxe at the entrence to the dungeon-if he's
up go kill him if not leave and reset instance.
The plans drop 8% of the time though I had much better results than that, he spawns 30-40% of the time.
To see how the method works in action have a look at the video here.