I know there are Web sites that deal with old house supplies and decorative hardware -- maybe one of them. There are several sites of people who make custom toilet seats, but they usually start with standard seat. Nevertheless, they might be able to help. Also check with local dealers of building supplies from demo'd houses; we have an outfit called "Broke & Poor" that has tons of stuff like this. Finally, Habitat for Humanity might have a store in your area dealing in used and donated items.
If all else fails, make one yourself, or have a local carpenter make one out of a good-looking wood. Do you still have the hinges from the old one?