From Bulbanews, your community Pokémon newspaper.
Code is 20150007, gives two Mega Starts
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The newest episode of Pokémon Get☆TV announced the first distribution code for the Nintendo 3DS eShop title Pokémon Shuffle. The code is 20150007, and when entered under the "Passcode" option on the in-game menu redeems two Mega Start items, which would normally cost coins to obtain. The code will be valid until until April 30, 2015.
Although it has not been announced outside of Japan, this code also works on North American and PAL region games.
The game must be updated to at least v1.1.1 in order for the code to be recognized as valid. (See here for how to update Pokémon Shuffle.)