Check out OSWRS (https://opensimworld.com/hop/82749; stands for "OpenSimWorkingRadioStreams"). You'll find ready-to-use radios, general ones that cover a variety of genres as well as specialised one. Inside these radios, you'll find station lists. And these stations are all pretty much guaranteed to work in OpenSim, otherwise Shawn wouldn't include them.
Have you looked at https://directory.shoutcast.com For any station there you can download the Winamp pls file which contains the URL you can set in OpenSim. I also have a free radio you can pick up that has quite a few stations worlds.quintonia.net:8002 in the shop there.