The Spring 2013 Meloetta was the only Western distribution for this Mythical in BW2. It was available from Feb. 23 to Apr. 19, 2013 in Europe, the Americas, and Australia.
South Korea, Japan, and Taiwan also had access to Cinema Meloetta (Dec. 19, 2012 to Feb. 28, 2013) while the rest of the world did not.
Fortunately, the Spring 2013 Meloetta is still obtainable through the DNS Exploit, which uses fan-hosted servers to access old Mystery Gifts. For help with setting up the exploit, reference our detailed guide. A Meloetta obtained through this method is legitimate and will pass hack checks.