Are you looking for the Owner's or Service Manual? Here's the link to purchase a Service Manual from Yamaha (I have purchased from them in the past for non-current sleds).
If you are looking for a repair manual, I purchased a CD off ebay that covers Exciter II 91 - 93 with some SX info. I don't remamber the guy's name but the CD goes by Repair Pro. I think I found it under Exciter parts.
hey max , i have one that i put together myself(photo-copied every page off one i got a lone of from my local yamaha dealer years ago) it is in a binder and the part # on the book is 8av-28197-jo. this is the factory yamaha service manual for the 93 ex570t/570et/570stt and 570sxt. i have no use for it anymore so i will give it you if you are willing to pay for the shipping!
The ebay # is 360028994637. I just did a general search for "yamaha exciter." I just got mine today and it seems to be pretty complete. It does cover the SX model too.