There are an incredible number of books on roses in general and heritage roses in particular.
Most rose people will have their own favourites - so from a purely personal point of view here are some suggestions:
Phillips and Rix The Ultimate Guide to Roses: A Comprehensive Selection (1 Oct 2004)
and TheQuest for the Rose
The Graham Stuart Thomas Rose Book
Botanica - Roses
Peter Beales - "Roses: An Illustrated Encyclopaedia and Grower's Handbook of Old Roses and Modern Roses, Shrub Roses and Climbers" - and several other titles
Several of the above titles are available locally but if you prefer your own copy then many of the recent and out of print titles above can be found on line.
Sources we have used include - www.amazon.com or www.amazon.co.uk for recent titles and www.abebooks.com and www.courthaybooks.co.uk for the older and out-of-print.
(Whereas a title search on amazon tends to be quite intuitive, abebooks title searches need to be accurate.)