In my experience, definitely from some internet outlet. If price is an issue, don't go to your local carrier store or the phone equipment section of a warehouse store. I found a net dealer who offered a usb extension cable, 3 m long, for what equals to app. 2 us dollars plus shipping.
To me it doesn't matter that it's an extension cable, i.e. it doesn't have a micro usb plug that goes directly in the phone. Instead I plug it in between the charger and the short, bundled cable.