I've been reading about Suzuki Shoshan, a samurai turned zen monk in the Togugawa era.

1. 'Warrior Zen: the Diamond Mind...' by Braverman
Inexpensive and easy to read.

2. 'Death Was his Koan...' by Winston King
Expensive, but goes into much more detail about the time period, politics of the day, as well as gives a serious critique about Shosan's 'zen'.