How do you get a lot of masterballs without cheats in Pokemon LeafGreen?

How do you get a lot of masterballs without cheats in Pokemon LeafGreen?
While you're exploring Sliph Co, there should be one that the president is holding it. defeat Givoanni and then talk to the president he'll give you a master ball. This is the only Master Ball that is obtainable in the http://wiki./Q/How_do_you_get_master_balls_in_leaf_green# without using cheats.