These are sites and companies that I have used and personally recommend:
Abes Audio (Australia) – HERE
Hardy Audio (Australia) – HERE
And sites and companies that others have recommended to me:
RadioCommercials.com.au (Australia) – HERE
Radio Copywriters by Earl Pilkington
Blogs, E-Books, Resources and Tools for Radio Copywriters, Radio Sales, Radio Promotions and On-Air staff who are also Radio Copywriters