When I went to purchase at bestbuy's website it ended up not being available. But there are a couple different ones available on amazon; I have the first one here:
Amazon.com: Peripheral / PAC IS710 5 Volt Charging Adapter for iPod/iPhone: Electronics
Amazon.com: ISIMPLE IS712 iPod 12 Volt to 5 Volt Charging Converter: Electronics
It works great. I still get a "this accessory is not compatible with this device" when I plug it in, but it plays my iphone through the factory system just the same as my ipod classic, and it now charges it at the same time. Isimple makes another ipod cable that I am interested in; it has the 30-pin connector on the ipod end, but a triple RCA output on the opposite end. I would be curious to see if you could get the factory nav screen to mirror the iphone screen using this cable, plugging the RCAs into the factory RCA inputs in the center console. I'm sure it's not that simple, but curious to find out.