Do any of you know a gambling company that has a good reputation and that accepts so-called 'novelty' bets?

I want to place a bet that a friend of mine -- who isn't famous -- will win a medal in the Olympics within 5 years from now.

I walked into my local betting shop, but when they accept a 'novelty' bet, it really only involves famous people, for example something like "The odds of Justin Bieber winning an Olympic medal before 2030". They typically don't accept a bet that doesn't involve famous people.

Can anyone suggest a gambling/betting company that will accept my bet? I don't mind what country they're based in, so long as they have a good reputation for paying out.