most (and I do mean almost all) radio stations have a streaming service of their own, or use something like iHeartRadio. So if you are just wanting to listen to music then that is the way to go.
If you are looking for something that actually picks up AM radio for the sake of recording it or something then you may be out of luck. I remember seeing some adapters back in the '90s that would do it, but I have not seen one in a really really long time. I am sure you could find one on ebay if you look hard enough, but I doubt it would work in a modern computer. It would be far simpler to get a dedicated AM radio, and then plug the headphone output into the line in on the computer if you absolutely needed to have AM run through your machine.