Factory Manuals
Here's where I got mine:
http://www.factoryautomanuals.com
Right now there are full sets of manuals listed on the website for 71, 72, 74 and 77 plus other sales literature and wiring digrams.
What's available seems to change every few weeks so check back. I initially didn't find what I was looking for and started perusing the e-bay adds. After getting frustrated I checked back a few days later - was glad I did because I found a greater selection. When I called to ask a couple questions a real car guy, his name was Bill, helped me out. He obviously loves his work and just wanted to talk about cars and of course books about cars. The folks who own the shop are named Dan and Deianna Bower. Their "About Us" page says that Deianna runs their church bookstore and "Factory Automanuals' business has grown beyond a one-man operation, enlisting the help of family and friends." The manuals came, as I recall, in less than a week via the postal service, though Bill told me I could choose UPS, the postal service was a couple dollars cheaper; they were exactly as described and boxed to make sure they stayed that way. Anyway, this sounds like a plug and I guess it is because my purchase turned into one of those rare experiences that was just a simple pleasure.
I also second Gummi Bear's idea regarding the CD version; I was thinking of going that route as well until I found this. Good luck; hope you find what you need.