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Which model of iPhone is this ?
If this is iPhone 5 or later model, then you can buy it from here --> http://www.ebay.com/itm/OEM-Lightning-To-USB-Cable-And-Or-Wall-Charger-Bundle-For-iPhone-6-iPhone-5s-/221955182024?var=&hash=item33ad8f4dc8:m:miYe8a6MLIB9h3DACluRJDg
The name of the cable is Lightning To USB Cable and Adapter/Wall charger.
If your iPhone model is 4S or lower, then you can buy it from here --> http://www.ebay.com/itm/OEM-Original-Authentic-Apple-iPhone-4-4S-3GS-30-Pin-USB-Sync-Data-Cable-Charger-/221948635847?hash=item33ad2b6ac7:g:YoQAAOSwHQ9WUrXW
The name of the cable for 4s or lower model is 30 PIN To USB Cable and Adapter/Wall charger. You can buy this from Amazon or other online stores.
If you have any questions or would like any additional information, please don't hesitate to ask