E-bay ocassionally has some listed, the manufacturer would be another place. If that doesn't work, look for websights selling aviation memorabilia, you would be suprised at what pops up there. US Air Force versions will be listed as -1 flight mauals or 06 job guides, civilian books are genarally named and numbered by the manufacturer. I have seen a number of L-1011 and DC-8/9 books on E-bay recently.
"Never trust a clean Crew Chief"