At this point there are no Nintendo games available for iOS devices in Apple's App Store. Nintendo has made it clear that they have no interest in releasing their titles for mobile devices like the iPad or iPhone.
Nintendo developer Takashi Tezuka said in an interview that it is "definitely possible" for them to create touch screen-based games, but they would only be released on a Nintendo platform.
Meanwhile, developers like SEGA and DotEmu have been hapily releasing other retro titles like Sonic the Hedgehog and Double Dragon for iOS devices. So there is no shortage of classic games available for the iPad.