In Japan, additional Wii U GamePad controllers can be purchased separately for more than $150. However, Nintendo fans in America won't be able to do the same.
Nintendo of America director of public relations Marc Franklin confirmed to Shacknews that additional GamePads will not be sold at launch. Instead, customers that want to buy another controller (or potentially repair a broken unit) will have to contact customer support instead.
Franklin noted that while the Wii U can support two GamePads, they will not be available for purchase at retail. As M2 Research senior analyst Billy Pidgeon pointed out to me, there are currently no games that take advantage of that feature. Offering a standalone controller at retail that serves no real purpose might cause retail confusion.
Nintendo has admitted that titles that support two GamePads will come "well after launch."