Is this what you are looking for http://www.famfamfam.com/lab/icons/flags/
Also have a look at:
- http://icondrawer.com/free.php
- https://www.gosquared.com/resources/flag-icons
- http://www.content-pack.com/free-flags-icons/
- https://github.com/stevenrskelton/flag-icon
- http://mdb-blog.blogspot.com/2016/10/list-of-country-flags-png-by-iso3.html
- https://dribbble.com/shots/1089488-Stripe-Flag-Set