Online Resources
The website internet-radio.com offers a .m3u file for each radio station to download. Download that file and open it with a text editor like f.e. notepad. The .m3u file contains the URL of the web audio stream. Copy that URL and paste it in MusicMateX when you add a new Radio Station. The website rcast.net offers the direct link to the mp3 stream. Just copy & paste the URL from the .mp3 link.
Search Engine for Web Radio Streams