This book. I'm sure many here, if not most, have read it. If not, I recommend it. It's great fun.
Is the author even alive? I'd like to suggest a few entries that are not in the latest (1997) edition. For example, 0.73908513321516064... which is... nah, I won't tell. See if you can find out what this is.
I haven't found any contact information, and his name is so common any web search is maddeningly cluttered.
Well, the first page of Google hits for
"david wells" mathcontains http://www.thetutorpages.com/tutor/david-wells-London-maths-tutor, which is the guy you're looking for. There's a contact form if you want tutoring, but perhaps you can try using it just to get in touch.