You can get a master ball in the hideout of team aqua in Liliycove city. I don't know the exact route, but the warp panels will teleport you to a place with 4 item balls, one of them is a master ball.
You can't get another master ball in emerald because there's no one will give you the master ball just the general will give you that.
master ball
a master ball!!!
You can't do that unless you have emerald. then you can clone the master ball.
Try harder
In emerald it is at the space station
958d8046a7151d70 8bb602f78ceb681a
In team aqua's base
no there is not
cheats
you can get a master ball in the team aqua hideout. Its in a room with four poke-balls.
you don't get the master ball from may in emerald, you get it in the team aqua/magma hideout in lilycove. that is the only way to get a master ball , unless you win the loto ticket drawing or use an actionreplay or gameshark.