As usual, replacementdocs is a good source for old games Cluebooks:
http://www.replacementdocs.com/download.php?view.6990
You can find map, install guide, other references there too:
http://www.replacementdocs.com/searc...ownloads&adv=0
I have never played Ultima, though. So I cannot comment on the quality of the Cluebook mentioned above.