There is no unlimited Master Balls cheat, but maybe you're talking about using an ActionReplay/GameShark. I wouldn't know about those. There is a way to duplicate Master Balls though, but that is only available in Emerald Version.
Master balls are the best kind of Pokeballs you can get on the game Pokemon. The cheat for unlimited master balls is to use the Missing No glitch.
You can't!you have to cheat
You can't have unlimited master balls although u can give the master ball to a Pokemon and duplicate it at battle frontier
with cheat code.
type the any Pokemon cheat
go to you tube and type it in
defeat team galactic commander cirus and get a master ball
You gain unlimited master balls, giving you the power to catch ANY Pokemon without fail, including all the uber legendaries, if you can find them.
you can use a game shark to get unlimited master balls
99 Masterballs in your PC: DCEEEC34AFEADC26 P.S. It may not work (only for rudy)
this is the code for unlimited master balls in pokemon flora sky F9AS0SL90D description master balls cheat, then upon activating it go to the market there you will see master ball for only 1.00
you get unlimited master balls by using action replay and put on master balls x999