On Iconspedia I have found this great set of round icons of flags of 231 different countries. To get these icons you have two options:
1-. You can enter the web and download it one by one click here
two-. You can download the complete compressed pack with the 2 icons in PNG formats (231 × 256, ICNS and ICO (256 × 128) to be able to see them and have them all more comfortably and quickly. The pack occupies 128 megabytes, that is, it downloads quickly .
Download: 231 flag icons