The mission list is basically a checklist (you can hide it by re-activating the entry in the terminal).
You have three paths to hunt them down.
1. Talk to Harper and choose the option to find locations without intel. From this she'll ask you how dangerous an area. The first major array (Hub Alpha) would be the least dangerous area - so she'll find a random one from that list for you. (After Alpha is destroyed, for Beta you would choose the 2nd most dangerous area, etc)
2. You can actually go to planets in those systems and hunt for listening posts - they are injected into the POI system so you can actually find them.
3. The intel you find from Watchtower bases and ships can randomly reveal the locations of listening posts in any...