Unfortunately, you can only get one of them. When you go to save mesprit, azelf, and uxie you will have to defeat Cyrus. Once you've defeated him, he will then give you a master ball. The only other way is to use an action replay code or something like that...
you can not get a master ball in Pokemon platinum only the one professor Rowan gives you
cheats
You can't.
cyrus gives it to you
no
Action replay
Yes there is a code for 999 master balls in Pokemon platinum
you have to have Pokemon platinum and a action replay then if u want just give your Pokemon master balls and trade them to games you want to have master balls
Go to your house and talk to your mum and ask in the microphone can i have master balls. don't listen
Pokemon lotery and action replay
Cyrus gives u one
Hacking