You'll find a copy of the Honda Factory Service Manual on the home page of our forum. It is very thorough, and an excellent reference.
The other two options are the Clymer and Haynes books. Both are still in print, and available just about anywhere. I got my Haynes manual at a local auto parts store, and I know the local MC superstore (Iron Pony) carries all the Clymer manuals. I seriously doubt you'll find either of these in downloadable format. They are in the print business, after all, and use print sales to finance the next project.
Hope this helps.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.