There are a few books that may be of interest to you with regard to your research and study of Filipino martial arts.
1. Campbell, Sid, Gary Cagaanan, and Sonny Umpad. Balisong: The Lethal Art of Filipino Knife Fighting. Boulder: Paladin Press, 1986. This is Grandmaster Umpad’s only published book. It is one of the early works on FMA knife craft published in the USA. It is still in publication.
2. Diego, Antonio, and Christopher Ricketts. The Secrets of Kalis Ilustrisimo: The Filipino Fighting Art Explained. Boston: Tuttle Publishing, 2002. This book offers a discerning look into the fighting art of one of the most highly respected eskrimadors of our time, the late Grandmaster Antonio “Tatang” Ilustrisimo.
3. Inosanto, Dan, Gilbert L. Johnson, and George Foon. The Filipino Martial Arts as Taught by Dan Inosanto. Los Angeles: Know Now Publishing Co., 1980. This book is considered a classic work responsible for the introduction of FMA to the martial arts community at large in the USA. If you can find a copy, consider making a purchase.
4. Wiley, Mark V. Filipino Martial Culture. Boston: C.E. Tuttle, 1997. This book is simply a must have for your martial arts library. It is a scholarly treatment of the FMA and the first modern work to take such an approach to the topic.
5. Wiley, Mark V. Filipino Fighting Arts: Theory and Practice. Burbank: Unique Publications, 2000. This book offers insights into 27 distinct systems of FMA. It is easy to understand and allows for the reader to cross-reference different fighting arts in one work.
6. Wiley, Mark V. The Secrets of Cabales Serrada Escrima. Boston: Tuttle Publishing, 2001. This book offers a clean treatment of the fighting art of another highly revered eskrimador of our time, the late Grandmaster Angel Cabales.
7. Yore, George M. Sonny Umpad’s Eskrima: The Life and Teachings of a Filipino Martial Arts Master. Berkeley: Blue Snake Books, 2012. This book offers a comprehensive treatment of the fighting art of yet another highly respected eskrimador of our time, the late Grandmaster Santiago “Sonny” Umpad.