You can get only one Master Ball in LeafGreen (as in every Pokemon Game) in the Silph Co. by Giovanni. Another way to get more Master Balls in LeafGreen, is to hack your game using Action Replay (if your game is in a Game Console, because there's another way of hacking Pokemon games if they are in your computer). Hope I helped :)
1 word: hacking 2 words: action replay 2 more words: Game Shark
Have your friends trade you the master balls they got.
Have a friend trade you a Pokemon holding the master ball they received.
well the max of master balls you can get is 999 but you can only get more master balls in trades.
No
give one to a Pokemon and trade the Pokemon with the master ball.
You trade Pokemon from friends that's Pokemon is holding a master ball
more like 493 master balls. its a cheat on the AR look up the code for it. its called Pokemon modifier.
Pokemon lotery and action replay
use a game shark
action replay