Honestly, the best place online (that I have seen, at any rate) that's dealt with this area - and indeed, the history of U.S. military/NRO activity in space generally - has been
The Space Review. Dwayne Day in particular does a lot of original research, and, yes, reviews of new monographs and sources.
Some highlights in recent years I might recommend:
The NRO and the Space Shuttle by Dwayne Day, Monday, January 31, 2022
Target Moscow: Soviet suspicions about the military uses of the American Space Shuttle (part 1) by Bart Hendrickx and Dwayne A. Day, Monday, January 27, 2020
Space myths: DoD and NASA cooperation by Wayne Eleazer, Monday, October 3, 2016
Review: Spies and Shuttles, by Jeff Foust, Monday, April 13, 2015
The HEXAGON and the Space Shuttle by Dwayne A. Day, Monday, October 31, 2011
Big Black and the new bird: the NRO and the early Space Shuttle by Dwayne Day, Monday, January 11, 2010
The spooks and the turkey: Intelligence community involvement in the decision to build the Space Shuttle by Dwayne A. Day, Monday, November 20, 2006
Part 2: The spooks and the turkey
There's a lot more where that came from. But hopefully that's enough to get you started.