Since I'm currently doing quite a bit of research for a new story, I thought I might as well share "the fruits of my labor" with you, so to speak.
First of all, the books. There is a novelization of T4 called "
Terminator Salvation: The Official Movie Novelization" by Alan Dean Foster as well as an official prequel to the movie by the name of "
Terminator Salvation: From the Ashes: The Official Prequel Novelization" by Timothy Zahn, both of which are available on Amazon.com.
I also suggest buying the
Terminator Salvation Soundtrack for creating the right atmosphere during writing.
Very helpful, too, is the
Terminator Wiki, especially its entries on
John Connor,
Marcus Wright,
Kate Connor née Brewster,
Sarah Connor,
Kyle Reese, as well as on the
Resistance,
Skynet, and the
Time Displacement Equipment.
Furthermore, I've compiled a
timeline of the major events of all four movies.
Finally, although there isn't a script or transcript for T4 available online so far, there are scripts for
T1,
T2, and a collection of early drafts etc. that can be found at
terminatorfiles.com. The site has also a
sizable collection of promo photos.
Enjoy.