The following sites (listed below) provide archival access to some well-known print and audio-visual ads. We also have quite a few collections of television commercials on DVD, as well as books on Advertising that often feature images of print advertisements. Try the search terms "television advertising" or "advertising".
Some companies or organizations will archive advertisements on their website. You may also be able to locate television commercials on the company's official Youtube channel.
The following sources provide additional insight in specific media channels. Some reports are updated annually, while others may have been "one-time only" studies.