first, put a lot of abuse on that guys ebay account. he sold you a car without the seats. that cable is completly proprietry, and it'll probably be easier to get it off the seller, than off apple, which is your only other bet, but i wouldn't have thought they sell these new cables in an Apple Store, or even on their online store, (i just had a look, and can't find it) this is the kind of stuff only apple certified repair centres get to play with.