Once you complete the Renown mission, that opens up a repeatable Support mission for the area. Getting a critical on that mission will give you a very rare doff and a refugee. Getting a success will just give you a refugee.
And you can find it either in sector space or Operations.
Geez what do I have to do to get a Crit? I put 2 blues and 3 greens, all Diplomats or Advisors, and all I get is a refugee. Twice. :/
It becomes easier the more purples you get. Also it's not always the best to have only diplomats. I experimented around a bit and now have two diplomats with 2 crit traits each, a fabrication engineer with 3 crit traits and a sensor officer and a warp theorist with 2 crit traits each for a crit chance of 32. So it seems that sometimes crit traits beat success traits.