You have 3 options:
1: Trade
2: Cheat it in
3: I'm Spiderman
(Hint! it's not number 3)
You can't catch Deoxys. You need to trade for it because it is only found in the Hoenh Region
You catch deoxys at birth island.
You can't catch Deoxys in Silver..
you have to get more then 45 gym to catch legendary Pokemon! deoxys is a legendary Pokemon
You can only transfer it as it does not appear in the game normally.
You can't catch Deoxys in soul silver
You get Tornadus from the Dream Radar app on the 3DS, or transfer it over from another game.
You get Deoxys through event or Poke Transfer.
You cannot catch a Deoxys in Pokémon White because it is not available in Pokémon White, you can only get Deoxys via official Nintendo event distributions as well as via trading.
No you can't catch deoxys by using cheats
You do not catch deoxys in Pokemon ranger shadows of almia.
This is not the way to catch Deoxys in Pokemon Emerald. You need an Action Replay or Gameshark in order to catch Deoxys.