The official Pokémon website announced today that the Lucario Wakuwaku Fair (ルカリオわくわくフェア) will take place through May and that it will be distributing a Lucario Secret Base Decoration at Pokemon Centers.

Unlike other events, this Lucario is not a Pokémon. It is a Secret Base decoration. The Japanese versions of Pokémon Diamond, Pearl and Platinum will be able to receive this item.

The Lucario Secret Base Decoration distribution will take place from May 1st to May 31st at all Pokémon Centers in Japan.

Source: http://www.pokemon.co.jp/pokecen/index.html