4gamer.net, a Japanese gaming website, has posted news about a new event item that has been announced in Japan. The event item is a Master Ball and is going to be distributed in the attempt to celebrate the release of the Official Pocket Monsters Black & White Encyclopedia Book in Japan, produced by Media Factory. It will be available in all six Pokémon Centers in Japan, starting from November 19, 2011 until March 3rd, 2012. So you have plenty of time to get it!

Look forward to this being added to our event database as soon as it's available, and also keep checking back for news on more events!

[Source] - http://www.4gamer.net/games/104/G010490/20111118037/