I want to run a story that takes place between episode 4 and 5.

The idea is, the players start on a prison ship and after a staged prison break they are recruited by a woman to help find her father that worked at a secret research lab. However first the players need to go to Corellia to get access to the research lab either getting help from the empire, rebels, or black sun. When they finally make it to the research lab they have to find and rescue the woman's father and then blow up the labs. The labs is infested with zombies from project Blackwing (from the Death Troopers novel.)

One problem is, I think Death Troopers was written after WEG stopped making sourcebooks... so none of them might have zombies in them.

You've got three great books already (can't comment on Dark Empire 'cause I never owned it), and 2nd Edition R&E is the best version of that game.

One sourcebook you might be tempted to overlook (but shouldn't) is the Death Star Technical Companion: it's just bursting with detail that can be used in all Imperial installations and ships, not just Death Stars (obviously).

Also, like Jareth mentioned, not enough good can be said about GG6: Tramp Freighters... though I think that one can still be a bit pricey, even now.

[EDIT: Hey, 1111 posts! ]

I want to run a story that takes place between episode 4 and 5.

The idea is, the players start on a prison ship and after a staged prison break they are recruited by a woman to help find her father that worked at a secret research lab. However first the players need to go to Corellia to get access to the research lab either getting help from the empire, rebels, or black sun. When they finally make it to the research lab they have to find and rescue the woman's father and then blow up the labs. The labs is infested with zombies from project Blackwing (from the Death Troopers novel.)

One problem is, I think Death Troopers was written after WEG stopped making sourcebooks... so none of them might have zombies in them.

As for zombies.....the only thing that even come close that I remember was an adventure published in Challenge magazine issue 46 called Imperial Research Station 13. No zombies, but definitely a horror adventure. If you can find it, it definitely fits the feel you seem to be going for. Here's the wookiepedia entry on it.

http://starwars.wikia.com/wiki/Imperial_Research_Station_13

But, WEG is such an easy system, that it would be very easy to stat the 'death troopers' yourself if you can't find the adventure/mag or want to stick with zombies.

[edit]

Just did a search, and if the adventure sounds like something you want, you can still get the mag for a couple of bucks on DriveThru.

http://www.drivethrurpg.com/product/87216/CHALLENGE-Magazine-No-46