Sorry. I've lived in a world where A/V means strictly composite. :/
(Seeing as most of the TVs I've played games on in my short life have called their composite inputs AV1 and the likes and many people have used A/V as a shortened way to mean composite compared to RF)
Either way, NES/SNES RF box. I don't believe a Genesis/SMS one would work, because those have the 8-pin plug on the end for going into the Gen/SMS. The TG16 has just a little round input for plugging the RF box in, which is exactly like the ones on the NES/SNES.
Your thinking of the Genesis 1/SMS composite jack which is an 8-pin plug similar to the VIC-20.
The RF jack of the Genesis 1/SMS is the same standard female RCA styled one used with the TG16/NES/SNES and the same RF adapter can work for all 5 systems.