you get the special key through the mysterygift
You find it in the Galactic Headquarters after they capture Azelf, Uxie, and Mesprit.
You will need Galactic key and this how to get Galactic key you will need to talk to a Galactic team mate by the Galactic HQ.
In the galactic warehouse to the left of the Galactic HQ
you go to the team galactic ware house
you have to go to the flaomora village and find the gate that is thesame when you got your starter pokemon and battle the galactic grunts and somoene will give you the key this is janbern P.alimes
then complete the stages and battle some galactic team members to find your self facing a galactic boss, he will then tell you where jupiter is with the three pokemon
simple answer go to Veilstone city and at the top right corner there is a team galactic building and in front of it there is a team galactic grunt talk to him and he drops the ware house key but here is a catch it breaks in the key hole after you use it and there is more doors so you have to find the galactic key... oh ya and one more thing the galactic key always works!
after you get galactic key go to the HQ with sattilite dish go to the door
The Galactic Grunt in Pastoria City has it. You need to bet the Gym to get it.
You find it in the team galactic storage area.
In the galactic warehouse.
In the team galactic storage house connected to veilstone galactic headquarters.