Oh, it exists all right. At least for the Nexus 8 hub, which is the she hub, isn't it? That's what I had on my Trek 720 at one point. I tried a couple different ways to put the grip shifter on a drop bar. It can be done, but not elegantly.
The hub on my folding bike, I think, is called Alfine; again, grip shifter.
Oh, that's right; I'm sure I saw one one of those before buying the J-tek barcon I have. They probably have the same inner diameter as the the Alfine trigger, which makes them unsuitable for most drop bars. Made to fit the skinnier flat bar diameter.
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● 1971 Grandis SL ● 1972 Lambert Grand Prix frankenbike ● 1972 Raleigh Super Course fixie ● 1973 Nishiki Semi-Pro ● 1979 Motobecane Grand Jubile ●1980 Apollo "Legnano" ● 1984 Peugeot Vagabond ● 1985 Shogun Prairie Breaker ● 1986 Merckx Super Corsa ● 1987 Schwinn Tempo ● 1988 Schwinn Voyageur ● 1989 Bottechia Team ADR replica ● 1990 Cannondale ST600 ● 1993 Technium RT600 ● 1996 Kona Lava Dome ●