Kurt, I'm glad to see someone watches these dérailleurs more obsessively than me. Nice photos, I've bookmarked those - keep them updated there's a good chap ;-)
I've never bought anything from cult-parts-freak but I have noticed over the last couple of years some very cool stuff -though mostly 80's and 90's eg. C-Record and Mavic (I love 90's Mavic -anyone have a seat-post for sale or a cassette? Ahem-sorry Dale) I imagine he's been selling too long to be moody.
Bob, there are actually 3 Juy 53's on eBay at the moment which is unprecedented in the last 4 or so years. check out eBay no's
300364936030 180421550135 110455236110 one of these is from Alexander von Tutschek but only one is NOS.
There was a rumour that these were *very* rare, but I think possibly just quite rare. I managed to score a NOS one from a small British seller a couple of years ago for under £100.
The correct double lever for the Juy 53 is for sale too; 110456084523 The seller has assembled it slightly incorrectly - the domed cover and wing-nut are on the wrong side of the levers but it appears to be all there missing perhaps a fibre washer or two.
I've got one of those too so I'm not in the market, but I keep an eye on it.
I believe (from Berto) that the Campag Gran Sport was introduced a year earlier than the Simplex Juy 53, but a year earlier than that was Huret. 1950 Competition front and rear cable operated derailleurs with double right side levers.These are rare also (probably RARE), there's also one for sale at the mo;
200402929238 I sold one on eBay a few months ago in really bad shape and I was embarrassed at how much it sold for.