Nintendo of Japan have put up the Wii U GamePad for sale on the online store. It is selling right now for 12,800 Yen ($104 USD). Now this does not mean you can buy a second one for your console, the Wii U only supports one Gamepad at a time. But this does mean if you happen to break one out of warranty, there are options out there.
As of right now, this is only up for sale on the Japanese Nintendo store, and no word yet if it will be coming to the North American or Europen stores. That said, it is still nice to see Nintendo moving to allow people to buy it, if they so choose.