I have plenty at home but alas currently archived in the attic.
"Beyond The Blue Horizon" is without doubt one of the best books written about aviation ever, if you can get a secondhand copy (there seem quite a few about) do so.
"Propliner" magazine issue 21 (so about 1986) has an excellent extended article on an Empire run from Southampton to Australia which Steve Piercy (it was his last Propliner) had dug out from the Flight magazine archives, first published there in about 1938. It featured a little introduction by the original author who was still around.
There is a large format book "Adventurous Empires" published about 10 years ago.
Sutton Libraries in London published several well done books about Croydon Airport (which actually lies within their borough) and Imperial operations during the 1930s.
There were a range of aviation books produced in the 1930s, aimed at the youth market I should think, which often tend to give emphasis to the Empire boats. I have found several over time. These are more likely to turn up in more generalised secondhand bookshops.
Then there are
these
And then you can download
this (right click on the Empire photo and Save Target As onto your PC - the instructions are not too clear but the resulting downloaded book is hopefully of interest.