Shadow Lugia (Japanese: ダークルギア Dark Lugia), codenamed XD001, is a
Pokémon exclusive to Pokémon XD: Gale of Darkness.
It says it's exclusive only to Pokemon XD, so no, you can't get it in another game unless you use a glitch or hack
http://bulbapedia.bulbagarden.net/wiki/Shadow_Lugia
