If you are luck enough to find someone that has listed a book as a source in their genealogy, a good way of getting that book is through the interlibrary loan at your local library. A good place to start is WorldCat http://www.worldcat.org/ to see if it is available. Your local library has their own network they work with. So if it shows up on WorldCat doesn’t mean they can get it but if your search pulls up a close library it increases your chances.
I like the advance search, but on the homepage your can enter a title, subject or person in the main search. When you find the book you want it will list whether it is a book, microfilm, computer file, etc… Click on the book you want, and where it list the libraries type in your zip code and click go. This will sort the libraries by how close they are to you. Take down the information like title, author and anything else you think your library will need & ask you librarian about it.
Two things to remember, not all libraries are in WorldCat and just because it is in WorldCat doesn’t mean your library can get it. This is just a way to increase your chances to find it.
Note: I have had family actually get microfilm from state historical societies via interlibrary loan, so that is another good source.