While he did not write books, you might be interested in these related topics:
* Books about James Montgomery Flagg: There are several biographies and art books written about his life and work.
* Books featuring Flagg's illustrations: He illustrated many books, magazines, and other publications. You can find these by searching for books with "James Montgomery Flagg" in the credits.
* Books related to poster art: Flagg was a prolific poster artist, and there are books dedicated to the history and development of poster art, including works by Flagg.
If you could tell me more about what you are looking for, I might be able to provide a more specific answer.