Another way to spot them in a large group is during the Zao Raid that takes place along the river there, starting right here:
then going right.
The orcs appear there in large groups along with Cublarc the Plunderer, which can drop a Disgusting Trophy! So both bestiary and a rare here :D
Just keep an eye on such msgs:
- 00:00: An orcish horde, ready for murder and plunder, is amassing to begin its travel through the steppes of Zao. Beware!
- 00:05: (unannounced raid)
- 00:10: The great march of the orcish horde has begun!
- 00:12: (unannounced raid)