Also, if you happen to have an older Wii that has the Gamecube controller ports, you should be able to use a GC controller as well, even better if you have a Wavebird.
Some Best Buys may still have the Rocketfish wireless Gamecube controllers too, though the stock locator was removed from the website. I think their base price was $14.99.
EDIT: I'm an idiot, I completely missed the point where you said you were playing on your Wii U, never mind...