u can only get one master ball in Pokemon Black to my knowledge, unless u trade with someone whose Pokemon is holding a master ball, or if u hack it, which there is no hack to.
you have to trade a Pokemon holding it to your game
You can only get lots of master balls by using a cheat/code. There is only one or two in the actual game
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 use the cheat.
Find an action replay code and program it, that's how you get many masterballs on Pokemon diamond action REPLAY. ;)
you go to the top floor at the sky pillar on emerald .you will need a macho bike and lots of ultra balls or a master ball
You can buy Game boy Advanced cheat games. You can then Click on the 999 Master balls cheat.
you have to have a R4.Which will give you lots of cheats
first you link you will need two game boy's and link it to any family or friends until you get inuf.
In Pokemon Emerald you can give one of your Pokemon a master ball and clone it. To clone, read this website : http://www.wikihow.com/Clone-Pokemon-in-Emerald You can clone up to 5 Pokemon. Note that this method of cloning is not 100% safe and your game may get corrupted.
First you get the one master ball then you either trade Pokemon with a friend who's Pokemon are holding the master ball, take it off, trade back and repeat this many times or you can use a gameshark or clone it.
You can get 1 master ball every time your Pokemon trainer ID number matches the lottery number perfectly, but it is very rare and their is no other way.