Request a 14-day trial subscription to the CalendariaLiturgica iframe service.
If you request is successful, you should see a link appear below. Using this you can download your unique readxml.php file (the file which your iframe will read from). This should be saved in some suitable folder, and accessed by your iframe. Your readxml.php contains your unique username and password, so should be kept safe. The file reads data from my server once a day, and saves that data as a daily snippet in the same folder, named snippet.xml.