hello michaelhaj, While I don't know of any places that offer free text books, there are several good internet reference sites to help study for the GRE. Here are a few that I found useful:http://www.grephysics.net
- full solutions and discussions to all of the practice GRE tests. (first thing to do, get all 4 ETS practice tests, and figure out what you need to study. Links on this site, among others)
There is a free physics text book available in .pdf format, although I can't really comment on it because I haven't read it. It is called Motion Mountain. Just looking at the chapter titles, I'm not sure how helpful it will be because what will really benefit your physics GRE score is doing lots of practice problems to improve your speed. http://www.motionmountain.net/contents.html
There is a book commonly called the REA "Purple Book", but the practice tests are generally considered to be more difficult then the real thing. That said, it is available used for a low price and makes for more practice. This website (physicsgre.com) has more info, comments, and resources.
Plan to spend a lot of time researching and looking, there is lots of good info already posted here on this website in the archives and articles, plus more. Then just go over the tests, take, and re-take them under test like conditions.