I'm going to try the Aberdeen university zoology building, the university library if I'm ever there. I will also consult hazelhead park pets corner(former site)
The University have a collection of the information, documents, records, press clipping, etc of the North East of Scotland Zoology Society (who ran Aberdeen Zoo) in their Special Collections. You need to make an appointment to view individual pieces (unable to view the collection as a whole), and they are not available for removing from the special collection section of the Library. As for ebay, in the past 5 years I have only seen one guidebook come up and it went for around £50. There are a handful of serious collectors in Scotland, who specialise in zoo guidebooks, so it can be quite an achievement to win it. Happy Hunting.