The Nintendo 3DS XL, a blown-up version of the 3DS, is receiving an add-on in the form of the Circle Pad Pro.
The original 3DS also had a similar peripheral released after launch, though due to the sheer size of the 3DS XL, you won’t be able to attach it to its larger body.
The 3DS XL Circle Pad Pro is coming sometime this year, reports Japanese mag Famitsu, as translated by Andriasang.
A peripheral you can reuse though, is the stand shipped with Kid Icarus: Uprising.
The Circle Pad Pro supports a few games including Kingdom Hearts 3D: Dream Drop Distance, Ace Combat: Assault Horizon Legacy, Uprising, Revelations, Metal Gear Solid 3D and Monster Hunter 3D (Japanese release only at the moment).