- The Apple Music app includes ‘FM’ radio streams through a built-in partnership with the TuneIn radio aggregator. I don’t think this requires subscribing to Apple Music, but as a subscriber I can’t test how it would be for a non-subscriber. Just search for the radio station name in the in-app Search field.
- Several third party apps specialize in forwarding internet radio streams worldwide. E.g. myTuner Radio, Radio.net, Pandora, etc. Search “radio” in the App Store, and you’ll likely find dozens generic tuner apps for thousands of stations each.
- Select radio stations may have their own app, which often isn’t better than the options mentioned above. Developing these for Apple TV seems more rare than for iOS.
WFUV says that they are available through TuneIn (Including the Apple Music app), iHeart Radio, or the NPR Music app. I could also find them on myTuner Radio and Radio.net.
WXPN says that they are available through the Apple Music app. I could also find them on myTuner Radio and Radio.net.
Both of these stations have their own app only for iPhone and iPad, but not for Apple TV at this time.
They all tap in to the same public stream, so the quality should be the same.

Apple Music app vs. myTuner Radio vs. Radio.net app