I have the 1996, 2000 and 2002-03 editions.
I worked for Walker's Manual in 2004 and 2005. A few years prior Harry Eisenberg had sold it to Andrew Berger, who is based in New Jersey. What I was told is Harry Eisenberg had a staff of six people doing research and the sales could not support it so he sold. Last I heard he still lived in the Bay Area. Andrew occasionally hired people on a contract basis to help on the book and projects. I helped input and edit the September 2004 edition which came out in paperback in mid to late 2005. He told me at the time that it was being sent to people who had pre-ordered and I assume pre-paid. I have never seen the paperback for sale anywhere. I have given away my extras. I do not think the 2006 edition was ever printed. If it had, I am sure Andrew would have tried to get me to buy one. Your best shot is to contact Walker's Manual directly regarding the paperback version.
They still have a web site.
I would be more than happy to interact with you, or anyone else, in terms of finding out more information on any of the unlisted stocks in the book. There are some real gems.