Did you order it directly from Disney? If so they can look up your order and replace it at Guest Relations at a theme park or at Downtown Disney.
If you bought your ticket from the Disney Store, if you bought multiples of tickets, maybe they can figure out which ticket it was by the ticket number.
These are the only options I can think of. Maybe others can help.
One of the most important things anyone can do is to photocopy both the front and back of any ticket they purchase. It is an invaluable resource to have if one does lose their ticket.