Right now there is no such search engine, although work is
under way - all credit to Gianfranco.
Meantime, You should search
Fictionwise and
BoB and the
Kindle store for the book you're looking for. If it's not there, it probably don't exist as an ebook.
Edit: Welcome to Mobileread. Here you will find people from all walk of life whose sole purpose is to help you make a smooth transition from being a regular book reader to being an ebook reading fanatic.