In your Sonos App, go to the radio station in question, and add it to your favourites.
Now i assume you already have set-up Sonos in Home Assistant.
In Home Assistant go to Developer Tools --> States.
Search for your media_player.whatevernameyougaveit
Under “Source” you find the radio stations you previously marked as favourite in your Sonos app.
Now to call it in an automation or something,
Use this:
Good luck!