Use the lottery
Transfer pokemon holding master balls from your gba games.
Go to the pokemon League then back to where you started go to jubilife city go to the contest hall and win,then when your done you should have 99.
If you do what the man in the house next to the pokecenter in solace town asks multiple times he'll give you one
You go to the soloman news press and give him the correct pokemon. It happens rarely.