Search in iTunes

If the iMac is running macOS Catalina or later, open the Music app, click in the search box at the top of the left sidebar, click iTunes Store at the top right of the main window.

Complete details are in Buy music from the iTunes Store - Apple Support

From what device?

If the following doesn't help, please reply with the device (iPhone, Mac, etc) that you want to search with.

Buy music from the iTunes Store - Apple Support