Go to the apple store nearest you and bring the phone and they will carry the exact one you will need.
At the auto dealership I buy my cars from I bought the car adaptor for both our android phones and iphone. But they charge much more. The replacement one I bought for my new car came from the Apple store. it functions perfectly.
http://www.apple.com and use the store locator feature or you can order it on line.
Actually its better to use Apple accessories on Apple devices.
I noted he asked about the connection. There is a non usb type and a usb type or a dual mode connection. I use the dual mode one. I think it cost me $40 but it works great.
Additionally for the iphone this poster needs it has a totally different connector than what I use.
Cannot go wrong with Apple Store but Walmart would have to charge the same price for Apple accessory since they have no price break per Apple agreement. And I don't think I would take a chance with a possible knock off part.