I don't know a master ball cheat, but there is a way of duplicating a Pokemon holding a master ball so u get two master balls and so on.
Um Who told you that cheat is probably a lair but it is true for the 999X master ball cheat.
you can get a master ball by winning the lottery in lilycove
you can if you have a Master Ball
In the Aqua Hideout.
Right of Lilicove
In lotto
i think you need a action replay card plug-in for gba sp and copy the code onto that
trade a friend a pokemon and his pokemon holding a master ball
With a master ball. It is the only way but to get a master ball you must cheat.
go on pokemon.com it will help u
die