I have such an adaptor right here on my desk. It came with a protable DVD player. The plug end has three rings and a tip connection. The other end splits into three RCA jacks. I've seen the plug on Adafruit, but I suspect that it won't be long before the
cable assembly will be available.
As for the GPIO connections... The first 26 pins have not changed. As long as your header matches up with those pins you will be OK.