Mavnet's fretted Custom was the missing one I was thinking of... the purpleheart-topped one with those cool birdseye maple wing inlays. That thing is amazing. Pretty sure that black (ebony?) fretless is his too, they were a pair.
However many there are, that's a pretty exclusive little group. Well worth tracking. I know Michael loves 'em, but I can sure see why the halt in production. My fretless Hyak isn't too far off these guys in spec, and that thing is a wrastlin' match. You really have to plan for it; posture, strap length, positioning, and it helps to have some natural reach. I have played a few gigs with that one, and it's a sweetie, but I'd never replicate it as a go-to. No. Way.