Are there even books for a 7, 8, and 9?
There aren't. When Lucas made the first movie (now called chapter 4) it was a low budget film that Fox almost didn't want to release because they didn't think it would make any money. When Star Wars first came out, there was no episode 4 at the begining scrawl. That was put in on the re-release the summer before Empire came out. Lucas had originally stated that there were 9 chapters. Well, actually he wrote the whole synosis as one movie, but realized that it would cost too much to do one 3 generation movie. So he broke up each idea into 9 chapters if you will, then tried to figure out which would be the cheapest to make. He decided that the 4 chapter would be the easiest to make as it would be the cheapest. He then set about writing I believe 7 different drafts for episode 4. He secured the funding with Gary Kurtz. He was able to do this as a independant film due to the fact that his just released movie American Grafiti was raking it in at the box office. Now Lucas himself didnt think that the movie was going to do what it did, and he thought that it would break even, and he would do another studio film, then take the money from that and do the next chapter. During the contract stages, he wanted both sequel rights, as well as merchandising rights. The studio had no problem with this as merchandising didn't make studios money, and at the time sequels rarely made money either. After Episode 4 was a hit, he realized he could make episode 5 on his own. He originally intended 9 movies, but realized that they would take too long. He waited 10 years after the release of Return or the Jedi to even think of starting to script the next, or first, chapter. He waited for digital effects to catch up to a point where he could do what he envisioned in his head, and while doing post production on Jurasic Park 1 (Stephen was in Europe shooting Schindler's List and asked George to oversee post production on the film and send him video daily's) that he now could do this. So he decided if he should do the last 3 or the first 3. Well he knew that doing the last 3 would entail new characters that no one would care about, or doing the first 3 for a back story that was already there, and character's that were already established. So he chose the first 3. It was at this time that he also realized that he didn't want to spend 16 years making 6 movies, so during the Special Editions, he decided to put in scenes in Return of the Jedi to effectively close off the series. So, in short, from what I am hearing, there will be no 7-9. There will be a TV series involving Bobba Fett in the works that is to start production soon and to show up sometime in 2006 or 2007.
The closest you will get to a continueation is the Paul Zahn books that Lucas had officially said in 1996 was the official continuation of the characters after ROTJ, but it is a story soley conceived of by Zahn, with sorylines and aspects approved by Lucas only.
mgctouch is right, the stories are of one families journey's through the eyes of R2=D2 and C3PO. but originally conceived, it was supposed to be a 3 generation arc starting with Anakin and ending with Luke and Leia's kids. Lucas was leary how aduiences would take the whole family thing and didn't even know if he was going to have it as a generational story while shooting Empire. I read somewhere that only on the day of the shooting of the scene between Luke and Vader did he decide to go ahead and have Vader be Luke's father.
But Lucas said there are officialy only 6 movies now. And since he will hold the copyright for a long time, he will make sure that no one takes the rights away and makes a 6-9.