FROM A DESKTOP WEB BROWSER
To export from Google Calendar, load up your calendar from the Google Calendar website. Then click on the small arrow next to "My Calendars", and click on "Settings."
That will take you to a page that lets you configure all your calendars. Look for the "Import & Export" subtab.
Once you export all your calendars you can clean up the file with only the events you want Gazelle to import. Unfortunately, Google does not allow you to only export a single calendar.