Manuals come in three types:
a) Owner's - comes with new vehicle or from previous owner if he didnt lose
it!
b) Service (shop) manuals from manufacturer, in this case Nissan.  SOmetimes
similar info is produced by a third-party licensed by manufacurer or not
licenesed at all - someone just makes up a CD. book, etc. designed to
replicate manufactyuer's book.
c) Repair manuals from well known publisher's like Haynes, CHilton, these
sometimes lag in time, i.e. there's nothing for my new 2004 Sentra and all
they offer is pre-2000 Sentra's from Haynes

My solution was:
a) I have Owner's manual came with a new car, obiosuly; but also:
b) MULTIPLE service/shop manuals from Ebay, multiple because no one was
complete and a few were lying (generic "car repair" disk, nothign specific
on sentras) but they were so cheap I dont complain ($12-20).  So do this:

1. Search Ebay.  Sometimes supercheap ($15 or less) CD's are a hoax good for
any generic car but not your specific model and not deep, just basic crap
extracted from websites, books, etc.  However my manuals from Ebay were 100%
OK.
2. Search Haynes
3. Search Chilton
4. Check manufacturer's website, perhaps call.  In my case Nissan explicitly
SPELLED OUT HOW TO GET Service (shop) manual in the back of User's manual
(guide), i went there and found cost $100's, so not acceptable for a single
person like me (OK only for a large shop or someone rich), so got from Ebay
instead (not Nissan's official, but similar).
5. Check helminc.com
6. Check www.courtesyparts.com/nissan-manual/index.html  Some (not all)
manuals there.
ALl about Nissan's manuals, parts, etc

Finally:
6. Search Web via Google, will return lots of false "hits" and
time-consuming -  the last resort however this is how I did  find all about
Chilton's, Haynes and helminc.com when I was a car moron seeveral years ago,
helminc still in business and I got owner's manuals from them, buit no
shop - shop was overpriced agagin.