Hey, Harbinger is a "secret" mission, so the mission node will not appear on the EDZ map until you clear the mission once. You'll need to manually launch the mission from within Trostland, in the building where the Hawk appears. In the second floor, there's a fireplace that may be blocked, if so use Hawkmoon to destroy the obstruction. Once the way is open, enter the passage and you should get a prompt to launch the mission. Alternately, you can join someone who already has the node unlocked and clear the mission with the.