Leon Rosser Jeep usually has them from 1990 or 1991, and you shouldn't have too much trouble there (
www.thinkjeep.com.) ChryCo Tech Authority lists from 1994 and up, and rumour has it they have earlier if you call and ask - searching here should turn up several instances of their 800 number.
It comes out to be worth buying the book - not just for copyright issues. I find it helpful to have the book handy, and printing them results in the need to keep a very large binder (or several small ones) around to be able to read the thing.
I'll stand by the "search" comment (tho that's not the way I'd have put it...) with a string of "FSM" or "Factory Service Manual" to locate the thing.
I've got most of the major books out there for the XJ - and I use my Haynes to level out the odd leg on the workbench. For the money, you're better off getting a Chilton's rather than a Hayne's until you can fork over for the FSM. FSMs also turn up on Ebay from time to time, so checking there may be worthwhile.
Expect your FSM to be at least two books (my 1991FSM is two, my 1989 is four - the later versions are singles) since they tend to break out the electrical stuff into a separate book, and there have been updates from time to time on drivetrain components as well. Later manuals (circa 1993-1994 and up) finally became single books (my 1999 is a single book IIRC, but I've not opened it for a while.) If you Ebay for your FSM, check the titles - or at least the number of books - to make sure you're getting the whole thing.
5-90
will be so proud of you. 
