en.wikipedia.org/…/Public_service_announcement

www.adcouncil.org
apparently they produce some of the more nationally popular ones. this specific page is about how a nonprofit can apply to be represented by the ad council.

samples of psa’s created by salo productions

aw heck, rather than relisting, just go to the external links listed at the bottom of the wikipedia article, to see more samples

american red cross psa samples

i’ll get back to this later. but from what i can see, if you simply google “public service announcements” you’ll come across hundreds of samples, which should be a starting point to get an understanding of what the best ones are, production techniques, distribution techniques, etc.