You can view all the flags here: http://hjnilsson.github.io/country-flags/
This repository contains renders of all the worlds flags in SVG and PNG format.
The source files were taken from Wikipedia and are not under copyright protection since flags are effectively in public domain (there may be other restrictions on how the flag can be used though).
The flags are named by their 2-letter ISO country code.
Also included is a JSON file that maps the ISO country code to the name of the country.
If you would like the flags in a different width than 250px, you can easily
use a combination of svgexport and imagemin from NPM to get that.
Run the following commands to PNGs of a desired width:
for file in *.svg; do svgexport $file "`basename $file svg`png" pad 1000: ; done
imagemin *.png ../compressed-pngs/
rm *.png
Replace 1000: with whatever width you want (note the :)