Just a quick note to refer readers to a long listing of dozens of Loch Ness Monster books and other cryptozoological items on eBay just now by seller roman10818. I don't think I have seen quite a good collection coming under auction from just one seller in my years of watching eBay. The listings include books from Gould and Oudemans in the 1930s right up to the present day and they can be found here.
Now I admit I own practically all of the Nessie items but I have been scouring the book landscape for decades. One item I did not own was an original copy of Frank Searle's unpublished "Loch Ness Investigation: What Really Happened", presumably posted out by Searle. I only have a photocopy given to me by one of Frank's supporters back in the 1980s.
The author can be contacted at lochnesskelpie@gmail.com