Shifter - Thumb - Sunrace Friction, (tandem drag brake lever)
Super cheap friction thumbshifters from SunRace. That's not such a bad deal, though, because yep they're cheap, but they're also reliable, durable, inexpensive, and they work great. No indexing, just friction, which is how we like them, anyway.
Can also be used as the drag brake lever on your Hubbuhubbuh tandem.
Includes a cable and a short length of housing.