I should probably be embarrassed for asking, but what are "butterfly shifters"? I do have a pair of Shimano Exage levers which clamp onto the handlebar and which have two projections around a central fulcrum, giving them a butterfly appearance.
If one really wants to keep both hands on the bars while shifting, good old-fashioned SunTour ratchet (non-indexed) barcons are a great solution, and compatible with any drivetrain.