Well, the US TurboDuo connector matches that of the PCEngine and PCEngine Duo's. There were official converter cables (I forgot the name, I think they were "Duo Cables") that allow you to plug in TG16 controllers in PCEngine. I don't know they're availability now, but I remember grabbing tons of them and TG-16 controllers and taps when Radio Shack was phasing out TG16 and Duo games and accessories. I did trade a whack load and kept some for myself.
You can make a reverse-tap as well. You get a TurboTap and a TG16-tap and swap the connector cables. Then you have a tap that allows you to use TG-16 controllers on a Duo/PCE and another that allows you to use PCE/Duo controllers on a TG-16.