I am also very interested in its historical existence. Unfortunately I have little information to offer other than what little has been made available on the web. The most compelling information I have seen about it is at
http://www.digital-brilliance.com/necron/necron.htm
- basically contending that the Necronomicon was written in the 8th century and not by H.P. Lovecraft but that no legitimate copies are currently in circulation.
Please let me know if know of or come across any more information.