I have a teacher that's leaving our school. She loves surfing and I wanted to get her some sort of surfboard you could sign (the size that can sit on a shelf) and ideas of what or where to get that?

you would probably have to have that custom made by a wood smith. It wouldn't have to be a usable surf board , just one to display. Carved wood, paint and a layer of fiberglass should do the trick to give it that authentic look. A sharpie would be needed for the signage.