they do not use a fiber optic head. They use(d) fiber optics to transfer the image into the hollow head. Disney World, to the best of my knowledge, is the only park that uses rear projection. Disneyland uses front projection.
I don't know of any place that would sell what you need. The best thing is to make it yourself. Get a solid head form and tweak it to work as perfectly as possible with front projection. Then use clear plastic to vacuum form the front of the head, giving you a clear, hollow shell. Give it a thin, even coat of white spray paint on the outside of the head so the projection will have something to focus on.
If you used white sheet plastic, not enough light would come through.
Anyway, now you have a front half of a head that can be rear projected upon. Place the projector behind it and use Leota's hair to conceal the fact that there is no back of her head while still leaving it open for the projected image.
When I was planning on using this method, I planned to have a witch sitting behind the crystal ball who would have the projector in her chest. Obviously, with rear projecton, the projector is now facing your patrons and must be concealed.