Hey your request is really hard to accomplish..
Because... in order to catch Deoxys... You need to catch all 200 Pokemon(s).
Then Deoxys will appear in the outerspace..
In order to go to the outerspace.. You need to go to the Mossdeep Space Center.

Then take to the man looking at the window and ask him if the rocket was launch successfully..
If he says:

more than 50% success: Jirachi's Lair
less than 50% success: Deoxys Lair

Hey before doing this.. You need to catch all 200 Pokemon(s)!!

Treeko up to Rayquaza. Then No. 201 will be Deoxys
while No. 202 will be Jirahi