Below we have a list of stores where both versions of the Wii U are sold out and where they are still available. Though for how long they remain available, we can't predict.
Best Buy, Toys R Us, and Target are sold out of both versions online. Sears and Kmart, which belong to the same parent company, are both sold out of the Deluxe version and don't appear to offer the Basic.
GameStop is sold out of the 32GB, black Deluxe bundle, but the 8GB, white Basic bundle is still available for pre-order.
Wal Mart is holding strong with both versions (Deluxe and Basic) still available on their own or as part of the Wal Mart Solution Bundle, which adds a Wii Remote Plus and a choice of a Wii U game to either system. The Solution Bundle is $400 for the Basic set or $450 for the Deluxe.