Premade list and dictionaries of all the countries along with their ISO 3166-1 alpha-2, alpha-3 and IOC letter codes.
ISO 3166-1 alpha-2: https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
ISO 3166-1 alpha-3: https://en.wikipedia.org/wiki/ISO_3166-1_alpha-3
IOC (International Olympic Committee): https://en.wikipedia.org/wiki/List_of_IOC_country_codes