Ok first go to socelan town or something like that. Go to the building beside the pokecenter talk to the guy on the left he'll give you an assignment after you get the pokemon save outside that building go in and talk to him and he will give you 3 of some kind of ball if he doesent give you a master ball keep reloading.
Go to the man in solaceon town becide the poke'mon center and he'll tell you to get a pokemon for him. Each time you get him one, he'll give you three types of a certain pokeball. Keep doing this until he gives you three master balls.
Trade with people and then go to the lottery place if you keep doing this eventually you will get a pokemon holding a master ball. OR you could go to a pokemon event and they give out RARE POKEMON holding a master ball. Or buy a game shark and enter a cheat code you could get 999 masterballs!
You turkey
No just go to the hq in veilstone city
What you do is go to the places behind pokemon league the fight arena and stuff and walk around there in the grass somewhere I got a master ball from just looking around
Go to the house right next to the pokemon center talk to the guy in the house find pokemon for him and he' ll give you 3 pokeballs of his kind keep doing it untill you get a master ball.
Go to a place in that tv town go to the lottery place if you win you get master ball I think