You cannot do that unless you have Pokemon rangers 2. So if you want another riolu you have to get Pokemon rangers 2.
Catch a Riolu and evolve Riolu.
You don't...
yes u can get riolu in Pokemon heart gold and soul silver you catch him or her in the safari zone and you can catch lucario in the safari zone two.
you can't- you have to catch pikachu and evolve him
No, not yet.
Floccessy ranch
You can catch Riolu in Challangers cave. You can't enter challangers cave till you have beaten the eliet four at least once.
You haven't made it far then. You can catch old pokemon. Yes, you can catch Riolu in the challenger's cave after you beat the elite 4. He's rare though.
Yes it is possible.
Safari zone.
Anywhere that you can catch Riolu. Shiny Pokemon can appear anywhere and anytime; with a 1/8192 chance of one appearing.
I am not sure, but you can evolve a riolu from a riolu egg that Riley gave you in Iron Island. Sorry if this is a bad answer!