I recommend you contact the Exhibition Study Group in the UK.
http://www.studygroup.org.uk/
(click on the blue 'please contact us').
They have members who are just as enthusiastic about the minute details of Crystal Palace, White City, Wembley, and Edinburgh, as many on this board are about the two NYWF's.
Mike Perkins and Bill Tonkin come to mind. I was pleased to be able to help Bill by contributing a little bit of useful information for his new book on the White City expos, and he filled me in with TONS of information including early drafts for the book.
I have Mike's book on the Wembley expo in 1924-25- it's an awesome work.
Bill and Fred Peskett wrote a book in 2006 called
The Crystal Palace 1854-1936 on Post Cards, so they are likely your best bet.
I'll PM you with the latest email address I have for Bill.