I don't want to bring your hopes down, but to be able to get Deoxys you need to get an Aurora Ticket. From an official pokemon event. Those are hosted by Nintendo, and they usually run for a week or so, in places like Toys-R-Us, GameStop and other known gaming places. They are rare and you have to visit Pokemon.com to find out when there will be one in your area.
Unless you get yourself a Gameshark. There is a code to get Deoxys in the grass anywhere, you can also go to Birth Island to find him there. There is no other way to get Deoxys, very sorry.