Help with lego star wars 3?

I have got reasonably far into Lego str wars 3 however I am trying to find out how to get a bounty hunger and a dark jedi and also a roboniho droid. I have been advised that you can build a ship in the level of the base but it keeps telling me I need more gold bricks, but I am unsure how to get these as I need the other characeters to get all the cannisters in order to earn gold bricks. can anybody help.