There is a way. I'm sorry if you have a DSI,(don't worry,I have one too)you cant do it.
You need action replay which breaks on a DSI. Every time you use action replay, you get a master ball.
There is actually another way to get one too, that is if you have another game (Diamond/Pearl) and another DS. You would have to play through the other game until Cyrus gives you the master ball. When he does give it to one of your Pokemon in that game then trade it to Platinum. Take the master ball from the Pokemon, then if you want to, trade the Pokemon back. If you want any more master balls you would have to delete the Diamond/Pearl game and do what I just said over again.
in solcecon town when you keep showing him the Pokemon he wants he give you some master balls
u go to the lottery and play each day until lottery no. matches Pokemon ID no.
Ultra Ball
from a jublife tv center or i dont know the name but enter the lottery if u got 100% same number you got master ball
You have to go to Jublife city and go to the TV station and draw a Pokemon Lotto ticket if any of your pokemons ID matches exactly you 'll be able to get a Master ball.
see the jublife city,go to jublife tv in the upper left walk inside then go straight if you get 5 digits in a row on you Pokemon id number you win a master ball or use action replay
you can not get a master ball in Pokemon platinum only the one professor Rowan gives you
there is no more masterballs in Pokemon platinum but not if you use cheats
no
well i do not now that
you need to go to the jublife TV station and talk to the lottery man and to get a Master ball you need to get the exacet same ID.number
you may trade with another person with a mater ball or you may go to the jublife lottery and if you have luck you may match up all the numbers and you will get a master ball :)