Falcon Friction Thumb Shifters
These thumb shifters are unusual because they fit on both road and MTB sized bars. Therefore, they fit on all handlebars. They even work on drop bars, but not on the sleeve.
They are not Campagnolo quality (what do you expect for $12 per pair) but they do function perfectly, and the soft rubber tipped levers are actually very comfortable. Cables are included. Price is per pair, a left and a right.