You can only get Deoxys through a trade or from past generations. You can catch it on Birth Island in Pokemon Emerald, or get it through a cheating software.
http://pokemondb.net/pokedex/deoxys
How to change your username How to add a user avatar Why was my post hidden? The points system Question etiquette Flags vs Downvotes Anime FAQ
Type a Pokemon name, type, move or ability to see instant results.