There is only ONE I believe.
one
1
You can only get one or use cheat
From the store
action replay
no
you can use a game shark to get unlimited master balls
You need to transfer from Emerald the mb. You give (Emerald) the Pokemon you are going to clone the master ball (hope you have 1) and then do the battle tower glitch and voila! Here are your master balls. You can use this as many times as you like!
Master Code: D8BAE4D9 4864DCE5 Buy Master Balls Code: 82005274 0001
No. However, you can clone a Master Ball on Emerald. There are also codes to get multiple Master Balls.
You don't.
you have to clone that Pokemon holding a master ball