None of the general Triumph history books I have found cover the new Hinckley Triumphs particularly well.
For my money there is one outstanding book that captures the essence of the history of Triumph well, and it has stunningly beautiful pictures.
It is "Triumph Motorcycles: A Century of Passion and Power" by Lindsay Brooke. My edition is the 100th Anniversary, 2002 edition. I don't know if there is a later edition or not.
Two sources to check are Amazon.com, (search Triumph Motorcycles), and motorbooks.com, (same search.)
Glad to see there will be an new Trumpet rider among us soon.
Monte