From the Lottories.
You can only get another masterball if a friend trades you a Pokemon holding the masterball they obtained.
Help silph co then talk to the president he gives the masterball to you.
Save Silph Co., Just like in Blue.
You run into entei randomly and use a masterball
The only way to get more masterballs without cheating is to have other leafgreen versions or firered or ruby or sapphire or emerald or Pokemon colosseum or Pokemon xd gale of darkness trade the masterball that those games get to leafgreen other than that you have to win the lottery in ruby and sapphire and emerald at lilycove city to get another masterball then trade it to leafgreen.
Once you have the masterball you get in leafgreen the only way to get another one is to have a firered or ruby or sapphire or emerald trade you a Pokemon that is holding a masterball.
you can use action replay code manager or you defeat Cyrus in team galactic warehouse and he will give you a masterball
Yes you can trade leafgreen version Pokemon to another leafgreen version.
you cant
mew-two is lvl. 70 in cerulian cave. make sure you save a masterball for him
There is only one masterball in yellow.
go into UN inhabited plain and go to the end and zapodos will be there