Doesn't really matter now - I finally found it. Most fun I've ever had blowing up a planet with a DS. I did the probe droid thing earlier, but with no success. The rebels had virtually no planets with defenses, so they were just moving there base anywhere the moment I showed up. I finally found it just scouring each system with my fleet (1 DS, 2 SSDs, 6 ISD2s, 4 VSD2s, 4 LFs, 2 ICs, ~400 fighters )