3DS XL Circle Pad Pro through its online store. The listing suddenly appeared two days ago, so we asked Nintendo if this was a mistake. A company representative confirmed with Joystiq today that, "yes, the posting is accurate and the accessory will begin shipping from our online store today."
We also inquired about availability at retailers; the previous iteration, the Circle Pad Pro for the original 3DS, was a GameStop exclusive. "There are no plans to sell this accessory at other retail locations at this time," the Nintendo representative confirmed with Joystiq. Online is the only way to get it – for now, anyway.
The 3DS XL Circle Pad Pro add-on is priced at $20, a peripheral that adds an additional analog stick compatible with games like Monster Hunter 3 Ultimate, Resident Evil: Revelations, Metal Gear Solid 3D: Snake Eater, Kid Icarus: Uprising and more.