A friend is a voice actor. She is listed with an agency.

Contacts are anything from adverts to video games to an interactive display in a science museum to a telephone "press 1" system.

If you have played a video game with a voice acting not from a famous performer/actor, those are typically done by professionals who specialize in voiceover roles, almost all these will be credited in the video game listing on imdb.com and the performer's contact or agency info is linked from there.

I (well my company) hired one before, we didn't need anything fancy or specific at all - just a professional voice.

She worked for a voiceover company, but I don't remember the name. We called her company up and said we needed xxx word narration.

The voice-over market has a lot of dedicated sites. Check out voices.com for one.

Fiverr, Upwork, plenty of places

voice bunny