There were a couple on the web, I think it was a Greenough Stage III. I was thinking of getting one, but I no longer own any boards with WAVE SET boxes. Those fins that Juan builds are really expensive from what I remember, but they are glass and not injection molded so those may be cheaper in the long run.
Erwin quit making fins about 10 years ago. He made the Hobie Dogbone and Waveset G&S fins. He used some kind of plastic that was stiff enough to surf with. More recently, there was a seller on eBay, something like "xhoserx", who made various repros, including waveset G&S, and Greenough Stage III. I've got one of his Stage III fins and it is super flexy, almost like rubber. Probably only good for a wall hanger. I haven't seem him on eBay for a while.