The Center for Public Integrity has created the MediaTracker database that lists the ownership of the nation's broadcasters. You can plug your zip code into the search.
The FCC maintains online databases you can use to find this information. Click on AM Query or FM Query at the link above. You have lots of output options if you're trying to incorporate these results into a spreadsheet or something.
You might also try www.radio-locator.com. For instance, here are the stations (and their owners) within "distant listening range" of
Spokane, WA. Basic searches on Radio-Locator are free. Other queries may require a
paid subscription. From personal use I've noticed that Radio-Locator will limit a particular IP address to some finite number of searches per day. It's less output friendly than the FCC search and possibly less up to date, but Radio-Locator includes links to stations' web pages, maps of broadcast areas, etc.