The JSF is very very very easy to get, if your neutral that is. As I have not done Rebel or Imp space stuff, I don't know if the requirements are different, but I would expect they are not. Once you have the neccasary lv for space, just follow these instructions.
All you need, is to be a imp combatant. (I was neutral in space, doesnt seem to have any effect) Get yourself over to Dath, and goto the Nightsisters village POI, near the entrance to the camp, you can find some bones laying on the ground. If memory serves, it's not far from the WP.
Examine the bones and you will find a item, something relateing to a possible Rebel attack.
Take this item to Kashyyyk, when you get there, look for the building just east of the starport. Go in, and speak with the Zabrak Imperial. He'll have you do a few easy missions, then send you down to the next level of the buliding, where you'll meet Vader. He gives you a space mission to do, and his JSF to do it in.
Gratz.. you just got yourself a JSF.
btw, you dont have to do Vader's mish if you don't want to. I just got mine a few weeks ago, so I'm sure this info is up to date.