For this particular research task, finding the location where the book was banned or challenged is very helpful. If for instance, you find that the book was challenged at a school in Chicago, Illinois, you can do some targeted searching for the book title in that location. Say you're researching A Clockwork Orange. You can type the following into Google:
You might also search to find newspapers in that particular region. Newspapers will be useful to you since they almost always get quotes from people on both sides of an issue. Using the same example, you may discover that Chicago's main newspaper is the Chicago Tribune and that their website is chicagotribune.com. Now you can do some more targeted searching using the "site:" command. For example, you can search for the book title and the word "challenge" just in that newspaper by typing:
Finding a newspaper article about your book being banned/challenged will greatly improve the quality of your research. For some books this won't possible, but for most it will be. See Ms. Pronovost if you need any help!