Tim,
did you try out this Bugatti site?
http://homepage.mac.com/bugatti/jacob/InfoHunt/
There are also the Bugatti books by H. G. Conway.
1.
BUGATTI 'Le pur-sang des automobiles', 1997, now in its fifth edition.
2.
Grand Prix Bugatti, 1983, last published in its second edition.
You can find these books at
http://www.abebooks.com/ but if you want to look at other out-of-print book stores, let me know.