“We would like to reassure you that GameCube Controller Adapter for Wii U has not been discontinued by Nintendo of Europe and we are doing everything we possibly can to meet the demand which is currently outstripping supply.
Nintendo of America hasn’t commented on the issue yet, but most likely the same remains true for this part of the world as well. Just be patient, and your GameCube adapter will find its way into your machine.
If anything, it looks like Nintendo underestimated the appeal of the GameCube controller. The device is the absolute best way to play Super Smash Bros. on any platform, and this is universally accepted as truth. Nintendo will come around to making sure every player has the opportunity to game as he or she sees fit.