It's hidden in Team Aqua's hideout.
you can get a master ball by winning the lottery in lilycove
In the Aqua Hideout.
Right of Lilicove
you can if you have a Master Ball
In lotto
die
You get the Master Ball in the Aqua base off of Lilycove. It is in an area with two Electrodes and one Gold Nugget.
throw a master ball
In the office of team Aqua's hideout.
Master balls cannot be bought in any Pokemon game.
it is in team aqua's base (the one where they had the submarine)
Somewhere in the aqua hideout (you have to be in lilycove city)