M$ Zoo Tycoon may be ported to Mac if there is a good sized market.
Click Here and, select
OTHER under
Product and then let them know what you want. When you get a response, post the email address (for direct access), along with the above link and then try to get Mac users to let M$ know that they would love to play Zoo Tycoon.
Do this on several sites, and you might be able to get M$ to do it.
After that, all you have to do is hope that enough people follow though and purchase Zoo Tycoon for the Mac to make it worth M$'s effort.