Go to the Poké Mart and buy a lot.
How do I get 999 Pokeballs? ( Anykind )
Go to www.supercheats.com and type the game in the search bar. Click on AR or GameShark codes. Just go through and find whatever cheats you need.
Go to a store that sells Action Replay DS (Walmart, GameStop, etc.) it's usually around $20, and it should explain how to use it, but once you know how to operate it, put your game in, and it should have "All Pokeballs in bag" cheat. Hope this helps.
Buy them.