The one that you get from prof. Elm is the only one that you get. Unless you use an Action Replay, you can only have one.
you will only be given one master ball.
no there is not
Well, as a Master Ball is extremely rare and it is has a 500% catch rate, there is only ONE Master Ball in the whole game so you can't get a Master Ball more than once without cheating!
maybe
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.
Have a friend trade you a Pokemon holding the master ball they received.
no you can not. its one and that's it. ONE
You have to use action replay.
if you clone a masterball
You can get more than one by matching all of the digits in the lottery.
In each game version, you can obtain only one master ball. So if you want more than one, you can consider trading or transferring a Pokemon holding a master ball from a different version.
Yes, you have to cheat or get match all five numbers in the lottery or trade with someone who has a master ball.