Hi Richard,
At a guess, I acquired over half of my military library from AbeBooks.com, some from as far away as New Zealand. A mixture of new and used, the only "grubby" one I have is "The Tiger Triumphs - The Story of Three Great Divisions [Indian] in Italy" - published in 1946 by H.M. Stationery Office for the Indian Government. Having looked for one for years, no matter the condition, I was delighted when AbeBooks listed one for only $34.00 - a chap I know gladly paid nearly seven times as much for a copy a couple of years or so back!
For anyone interested here's the catalogue of my military library:
http://www.northirishhorse.org/books.shtml
Cheers, Gerry