From a Toys R Us ad, unconfirmed at the moment:
Register a 2DS or 3DS XL and one of Super Mario 3D Land/Mario Kart 7/Animal Crossing: New Leaf/Donkey Kong Country Returns 3D/LEGO City Undercover: The Chase Begins/Yoshi's New Island between March 1 and March 31 and get a free download copy of Pokémon X or Pokémon Y.
(Source)
Register a 2DS or 3DS XL and one of Super Mario 3D Land/Mario Kart 7/Animal Crossing: New Leaf/Donkey Kong Country Returns 3D/LEGO City Undercover: The Chase Begins/Yoshi's New Island between March 1 and March 31 and get a free download copy of Pokémon X or Pokémon Y.
(Source)