Here are some ways to get items that can be used to help you catch Pokémon in Platinum:
* Poké Balls: You can purchase these at Pokémon Centers or find them in various locations throughout the game.
* Great Balls: Can be found in the Trophy Garden after completing the National Pokédex.
* Ultra Balls: Can be obtained by winning the Battle Frontier or purchased from the Poké Mart in Veilstone City.
* Master Balls: These are very rare and can be obtained by winning contests or by using a cheat code.
Remember, the best way to catch Pokémon is to use the right Poké Ball and weaken the Pokémon before attempting to catch it.