Google Chromecast audio normally is not able to accept directly radio streaming address but there is a nice and easy way to send radio streaming links to Chromecast audio using an android phone/tablet with the RS_player APP that you can download from here.
RS_player is easy to use. You need to have an account in www.iptv-updated.com. After you have to organize radios in each country group.
- you can create manually the radio adding the link (m3u, mp3,..)
- you can search the radio from the internal search engine and add it in your personal account
All Radios added in your account (created from you or added from internal search engine) are also visible in the Android RS_player app (in the tab remote channel, after that you are logged in).
In RS_player you can also organize your radios in the favorite playlist.
All the details on how to configure RS_player is here described