For your advertising case study, if you are looking for advertisements, the ProQuest family of databases has an ability to limit your search to advertisements only.
To access ProQuest databases, go to the Databases A-Z page and choose "ProQuest" from All Vendors / Providers menu:
Choose one of the databases that best fits your topic and click on title to open database.
To limit to only searching advertisements, go to the Document Type limiter and click on button next to "Advertisements":
Then enter search terms.
Look at your search results for advertisements: