veilstone city but first go to pastoria city hope it helped.
bad guy HQ (team galactic) is in Veilstone City
go and catch them
after you get galactic key go to the HQ with sattilite dish go to the door
beat the leader.
Its in the town of Veilstone
You get a Master Ball from Team Galactic Boss Cyrus at the Galactic HQ.
Cyrus is in the galactic veilstone HQ and spear pillar.
Fast way is to use a escape rope or telaport
Looker eventually gives you one
nothing just beat the galactic HQ in Pokemon pearl and diamond
In the galactic warehouse to the left of the Galactic HQ
You Go to the building next to Galactic Veilstone Quarters and Follow the track until you meet Cyrus, The Leader of Team Galactic