You can't get a deoxys in Pokemon pearl..But, u can migrate it..
To get deoxys u need an aurora ticket or Ill tell you a secret go to Mossdeeps space center and talk to the guy whereing a white gacket and if he says no 56,59 or 99 you could go to the moon and you see jirachi and if you battle it and catch it then look around the moon and you will find Deoxys.