The only way I can think of is to navigate to their website from a computer, and either right-click the button/link on their webpage that launch the radio through HTTP and grab the stream URL that way.
If the link for their URL stream isn’t available through that solution, I’d recommend listening to the radio on your computer, switch to the window containing the radio (the player window), and then (if on Safari on Mac, at least) go through the code with the Encoding option in the top menu bar.
The stream URL should be there, for sure.
Great to hear it works.
How to launch in the Music app through a Workflow.is workflow… hmmm… I’d have bet that either Google might be able to help, if not anyone in here