Lucario, along with Riolu, are some of the most popular Pokémon ever, so players want to know where to get them in Pokémon Brilliant Diamond and Shining Pearl. The good news for all Lucario and Riolu fans is that they are available, but it is only from one place.
Players will need to play through the game until they reach Canalave City, which appears quite late in the story. You will be given the chance to take a ferry over to Iron Island by speaking with a sailor near a boat. Once you get to the island you will find a cave.
Head inside and you will find Riley, you who request some help from you. Riley has bitten off a little more than he can chew and you will need to take on some other trainers with them to get out of the cave. Once you get Riley out of the cave, he will offer you an egg to say thank you.
This egg will spawn a Riolu after you walk with it enough, and is the only way to get Riolu in the game. Once you have Riolu, you can work on evolving him into Lucario by getting him to maximum friendship. You can do this using something like the Soothe Bell. As soon as he hits maximum friendship, the Riolu will evolve into Lucario.