I bought mine from
www.dascheap.com/ but if you live anywhere outside the continental US, I do
not recommend you buy from them. I'm in Canada, and they me jump through a lot of hoops for them to provide them with a written signature and the phone number to my creditcard branch so they could "verify" my identity. I've bought from tons of online sellers and never had to do anything so ridiculous. And then when they did confirm I'm who i say, they charged me over $30 to ship the unit and when it arrived, I had to pay $20.58 additional import taxes. bastards.
Anyway there is a Genesis adapter that's sold separately. its a pretty standard GOAC in every regard except that it uses the SNES as a base for power supply and controls. The video is handled by a completely separate composite video cable that plugs into the device itself. I dont have one because I only have a small library of Genesis games, plus I still have a CDX.