and not even that is necessary, two weeks ago ( some 2350 Ly from Merope, Northwest of Bubble ~ y:+950 I had three Systems with multiple Planets with "non human signal source" (Tharg Sensor) - neither of the Systems had a GG or any other Planet/Moon with Ammonia Atmosphere..... They just happenUnfortunately, no. They can be found anywhere in the galaxy, as long as the system has a Gas Giant with Ammonia-based Life.
Now, it's time to drink!