I've only found it by accident. I was actually flying to a waypoint behind S21. If I was to hide something, I'd place it there because nobody ever moves behind S21.
Just kidding, Loken and St. Denis told me directly. Skorak as well. Then I used my cheats. Then I wallhacked into the station and looted the 1500 Sci-Data. Then I claimed the station inRP for my new faction, which needs a Core 5 POB. It's gallic.