I found a booking agency which handles booking for David Bowie for
speaking and entertainment engagements. On their website they say they
will give you a price and availability quote within 24 hours.
"The Allen Agency, Inc. offers a selection of over 3,000 Professional
Speakers, Celebrities and Entertainers for corporate events and
fundraisers. Actors, Comedians, Television Personalities, Sports
Motivators, Authors, Musicians, Political Figures and Business Leaders
are available. Type in the name of ANYONE you desire on our Celebrity
Request Form (whether or not you see them listed) and we'll get back
to you within 24 hours regarding fee and availability. For immediate
needs, call us at 800 516-9090."
Luckily David Bowie is listed in thier catalogue of speakers, so you
might have luck.
If he is not able for attendance, I would ask the Allen Agency if they
could arrange your other request. Perhaps the Allen Agency would be
able to work something out considering they handle other requests of
artists. Unfortunately, there is no official fan club at the moment
and hence I do not know where you could personally write him other
than his house address in England. (due to the terms of service of
this service, I cannot post his mailing address even though it is his
only fan contact portal right now). You can try joining the discussion
groups on his official webpage, and he does take questions and answers
them there. Hopefully your heartfelt request will be noticed by him or
by one of his assistants. The website is here:
Best of luck arranging this birthday party, and I'm glad I could help.