Got to love Bigmouth. They've got probably the largest range of voice actor talents in New Zealand, and they have a huge range of pedigree clients... visit their website and listen to the samples. There's a wide range of voice talent, young, old, male and female - so there's bound to be someone right for your advert.
I've had a few friends who've personally dealt with Bigmouth and have been very happy.
PO Box 60189 Titirangi 0642