Recommendations for English Voice-Overs in Multiple Accents

I have need to have some English voices recorded but in multiple accents (British, American, European, African, Malaysian, and Australian). Matters are complicated further by the fact that most of them have to sound like they are coming from older teenagers. 

I am really struggling to find a voice over agency that can help. Does anyone have any experience of one they think might be able to assist? Essentially, I just want to provide them with the script, and then have them return sound files back to me.

Thanks in advance!

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