It's actually far more specialised and difficult than you would ever dream - which is why the proefessionals make literally millions doing it.
A lot are actors, and the competition is incredibly fierce, so agencies tend to use the same top ten per cent, who clean up ninety per cent of the work.
You could always try your local radio station, but chances are, they buy ads in from a national agency, and that's the problem, the top people have it all sewn up.
Sorry to be a pessimist, but that's the benefit of my personal experience, based on the same scenario.
If you do crack it, come back and tell me how!