I'm afraid you can't. Although if you have a friend that has it on emerald, firered, or leafgreen you can get one by trading. Good Luck!
you might have a chance at codejunkies.com
bird island
if you want deoxys well its bad for you cause you can only get deoxys in janapese version.p.s.its only in ruby,emerald,sapphire,and others i forgot but not in leaf green or fire red
I have no Idea about it on Ruby But I do know its on emerald. But My brother was talking about Deoxys on Ruby so Its a 50/50
Unfortunately you can't get it on the original version of Pokemon Ruby, you have to have the Event version of the game called Pokemon Ruby Deoxys version. Pokemon Ruby Deoxys version- After beating the Team Magma in the Space Center read the sign it will say: Accepting rides to the moon for trainers! Talk to the Space Center Manager he will let you go to the moon, SAVE, and go up there will be Deoxys. Make SURE to save cause if you faint it or run away it will disappear forever Pokemon Emerald- with the Aurora Ticket from an Event head to the SS Tidal in Slateport City or Lilycove City show the green haired lady the ticket, they will take you to Birth Island, complete the puzzle and Deoxys will appear at level 30.
You can't find one you need to trade one from FireRed/LeafGreen/Ruby/Sapphire or Emerald
Get a Deoxys in Pokemon Emerald, Ruby, Sapphire, Firered, or Leafgreen using the Mystery Gift, and migrate it to your Diamond Version.
Blooduh
You can't.
To get Deoxys, you have to migrate from leaf green ruby fire red saphire emerald versions, just to get Deoxys
Use this gameshark cheat code Deoxys 8C5DE8C8A33E9D88 or C5946A0E65BE02B0 or FBC061A9072FC320
NO!