Your watch will never have an "original" crown again. It can have a "correct" and "authentic" crown, but "original" is gone forever once the part that it left the factory with is lost / replaced. Just want to make that absolutely clear, as I do with nearly everyone that uses the term "original" incorrectly.
A watchmaker could find you the correct one from Omega with the case reference number. If you can find a decent picture of what shape the crown is somebody here might be able to help. Actually, most of us could if we felt like doing the homework for you. 馃槈