Here's why:
* PP Restores are a Gen 4+ item: They were introduced in Pokémon Diamond and Pearl, which came after SoulSilver.
* SoulSilver uses Gen 3 mechanics: Therefore, it doesn't have PP Restores.
What you can find in SoulSilver:
* PP Up: Increases the maximum PP of a move. You can find it in the Safari Zone (rarely) and at the Celadon Game Corner.
* Ethers: Fully restore the PP of one move. You can buy them from various shops.
* Max Ethers: Fully restore the PP of all moves. You can find them in the Safari Zone (rarely) and buy them from various shops.
* Rare Candies: Raise a Pokémon's level by one. You can find them in the Safari Zone (rarely) and buy them from various shops.
Remember, you can also use healing items like Potions and Revives to help your Pokémon recover from battles!