Is there a way to have a chance of getting a female riolu?

No. Sadly you can't become a female Riolu when you first start the game. Only a male(which kinda sucks, but eh.) But to recruit a Female Riolu in the game, yes you can. It'll be hard but you can.

You can recruit one in Crystal Cave. If you find a Riolu (which has a low appearance rate), there's a 1/8 chance it's female. The recruitment rate for one is low as well.

For starters I don't think it's possible but you can always pretend to be male, I do that all the time in the games when I want a male starter like Riolu.

I'm a girl and wanted to become a female Riolu as the hero, so what I did was used a cheat on the female Pokemon I became.

Here's the code: 122B5158 000001E9

And here's one if you want it as your partner: 122B51C0 000001E9

All you have to to to have it as a female is to choose any female Pokemon as your partner, then hit (Select) in your game and it will show you or your partner as Riolu in a dungeon, then save and it will be permenant.

If you have a physical copy of the game, ( Not saying you don't or not ) why not just add the female symbol at the end of their name. Like I heard gender doesn't matter in the game, more of personal preference. So if you don't like looking at the stats, I think it will be fine.