Schlumph makes something like this, I think. I think it's only 2 speeds.
I think what you really need is a Shimano Integer front freewheel crankset, they came on some old Bike Boom Schwinns. They got kind of a bad rap because they were paired with the Positron "indexed" derailleur but it was actually kind of a neat concept. I keep wanting to build a bike that can use one but they take a bigger cup like you use on a Ashtabula bottom bracket.
You might have to end up having to fab your own custom hub.