This Repository holds a sample ics file, acting as external sample subscription calendar file for the Add to Calendar Button demo page, which is available at add-to-calendar-button.com.
With the Add to Calendar Button, you can also offer your users the option to subscribe to a calendar, instead of only saving static events.
To get this to work, you would simply need to set the public address (an .ics file) of the calendar as the "icsFile" option and set the "subscribe" option to true.
This repository holds a demo ics files.
Check out add-to-calendar-button.com/en/advanced-use#3 for more details and the actual demo.