in veilstone town
you have to keep following him
its in veilstone city and its quite big - u cant miss it.
In Diamond you can get Dialga, but you find him in the Spear Pillar after you beat Cyrus of Team Galactic. Im Pokemon pearl you find Palkia.
Beat Cyrus in the Team Galactic Veilstone Building. He'll give you a MasterBall
CYRUS IS THEN IN GALACTIC HQ WHEN YOU FIND HIM YOU BATTLE HIM IF YOU WIN HE GIVES YOU THE MASTER BALL. (The master ball should go to the FIRST Pokemon in your team)
can find one in the team galactic warehouse or head quarters in Veilstone city When you have to free the three Pokemon they captured.
You'll find him on the top of moutain Coronet. But before you catch him you'll have to battle team Galactic.
In stores.
Back of Veilstone City
veilstone team galactic base veilstone team galactic base
in the storage place in veilstone is the galactic key, u just gotta find it.
you can't only in Pokemon black and white.