Pokémon Brilliant Diamond & Shining Pearl:
* Breed: Riolu is the evolution of Lucario, and you can breed a Lucario with a Shiny Charm equipped to increase the chance of a Shiny Riolu.
* Trade: You can trade for a Riolu with someone else who has one.
Pokémon Sword & Shield:
* Catch: Riolu can be found in the Lake of Outrage after defeating the Champion and completing the Postgame content. It is a rare encounter.
* Trade: You can trade for a Riolu with someone else who has one.
Pokémon Legends: Arceus:
* Catch: Riolu can be found in Crimson Mirelands during the Postgame content. It is a rare encounter.
* Trade: You can trade for a Riolu with someone else who has one.
Other Pokémon Games:
* Trade: Riolu can be traded in most Pokémon games, so you can check with other players or online communities for someone who is willing to trade.
Important Note: In most games, Riolu evolves into Lucario at level 15 with high friendship. Friendship is increased by battling with Riolu, walking with it in your party, and using items like Friendship Berries.
If you are looking for a Riolu in a specific game, it's best to check the official Pokémon website or a reliable game guide for the most up-to-date information.