What terminal are you going to? Terminal 4 has a small b-store (Hudson Books) with magazines and mostly top selling books.
Click this link for a list of Terminals:
LAWA Terminals
Then click the terminal you want, next look for Retail or Shopping. It will likely be a Hudson News or Books.
Beyond that, there's a Border's Bookstore South of the airport about 3 miles, but you'd need a taxi or other transport to get there:
Google Map LAX to Borders