You can order the book here:
http://sepalms.org/SPS_Publications.htm
Its formatted like a Magazine, and It costs 12 dollars plus 2 in postage and it is probably the only and best book(let) in the world for reading about hardy citrus growing and varieties. I have worn my own 2004 print totally out, it is a very good read when you are interested in this topic.
Tom McClendon wrote the Hardy Citrus book, and he did a very good job. He is a experienced amateur citrus grower, and he grows citrus in two differen gardens in different zones. One in relatively continental Central Georgia and on in a much milder coastal garden. A lot of the Hardy Citrus varieties that you never heard about are described in this book, along with cultivation, propogation, hardiness, diseases and other relevant topics.
Order You own copy now ! it beats fidgetting around with incomplete prints or digital versions.
Bernhard Voss has also written a couple of books about citrus, that have a special mention of hardy varieties and growing hardy citrus, but his books are in German language.