I have a saved eBay search for used examples, but absolutely nothing has come up for the basses. I own these two beauties, the design works brilliantly for skinny-string. A real shame it hasn’t translated to bass.
A couple of my friends had these when I was a teenager and I really wanted one! Ended up picking up a demo MkI TRB6 (amazing instrument, still have and love it), but never got to scratch this itch!