Chris,
Hans Seegers "Grey Book" is the corner stone of most written advice .
the main text is in german but the book is extremely well illustrated and all photographs taken a detailed caption in both german and english.
The chapter on large size binoculars is written in both german and english.
if you ant the text in english - good news Dr Seeger has allowed themajor chapters to be translated and reporduced on peter Abrahams website.
( You can also join peter's mail lists which provide a written update on a regualr basis ).
Hans Seeger has updated his book when last published ( 2 years ago), and it now contains some "red pages" - a comprehensive listing of Zeiss binocular types , batch numbers , numbers
produced per batch , and the number of each type known to the author.
( A lot of collectors send Hans S. serial numbers of Zeiss sets they buy- in itself this is an important data base.).
http://www.zeisshistorica.org/index.html
http://home.europa.com:80/~telscope/binotele.htm
( Peter Abrahams site , you can sign on for his news updates at :
Peter Abrahams
abrahams.peter@gmail.com or
telscope@europa.com .
Zeiss have a historical society which has an on line membership.
Dr Seegers Book:
Fernglaser und Fernrohre in Heer, Luftwaffe und Marine.
Military Binoculars and telescopes for land , Air and Sea Services
By Hans Seeger.
ISBN 3-00-000457-2.
The book covers optics of all nations. ( Mostly German , British , American , Japanese, Russian , French and Polish).
This book can be had in the US from Deut. Optic and from various sites on line.
"
A Guide to hand held Military Binoculars" By Dr Steve Rohan.
Photographs and text in English describing most binoculars you might encounter , characteristics of all sets given , eg weight , size , field of view , type , if lens are coated , and rarity of the set within the USA.
"Eyes of the Wehrmacht" By Steve Rohan- this deals mostly with the 10x80 flakglas and large Zeiss models.
Both published in the USA - I picked mine up via eBay.
"Fine Binoculars of the 20th Century" By R C Gregory M.A.
ISBN 0-9544050-2-1. Published privately by the author. ( Ardwell books Tel-01582832152).
The author describes binoculars known to him by power size - a photograph description and the authors opinion on the sets , "warts and all".
"We are certainly not afraid of Zeiss" By William Reid.
( Barr and Stroud Binoculars and the Royal Navy ) - the history and products of this major british opitcal firm - an excellent book).National Museums of Scotland Publishing Limited.ISBN 1-901663-66-3.
Well illustrated with excellent descriptions of all sets known to have been amde by the company.
(Hand held).
All of the above can be traced via P.A's site.
A post on to Peter and placed on his lists will probably put you in touch with the authors.
Brett is correct regarding eBay although prices depend on who is bidding on the day.
Some reliable eBya sellers. ( In my experience ).
Anoraksia - Mike Palmer - Uk based - honest and reliable.
Bino_Mania - Ray Dann - a collector and honest man.
A lot of sets will come from private sales or general sellers of militeria - be sure to ask plenty of questions regarding the condition of the sets and beware of some descriptions - Brett has already mentioned " Afrika Corp" - U-Boat is another , "Ultra rare" , "must be rare" "Panzer Binocular".
A few months back I saw a set described as being " Genuine Africa Corp U-Boat , SS binocluars" the seller covered every base !
Often sellers may not know much about the set - and one or two big time collectors who will remain nameless will "make them an offer they cannot refuse" and the sale is live one day and gone the next , hardly fair but money talks - the way of the world.
Attached a photo of hans Seeger's "Grey Book" that on top a 10x45 sight for a 4 metre range finder - it is decribed inside the book.
Sorry for the long blurb which I hope might be helpful. ( Sermon over

).
One good way to pick up info - there are a few good guys who post on this forum Brett , Le Bretton , being two who spring to mind - bouncing ideas and opinions of people - it has helped me quite a bit - I certainly don't stand here as an "expert" - I too have been stung once or twice and sadly there are rogues out there.