In my case my requirement was slightly different: I needed to figure out whether any given ISO code belongs to the EU, but the idea is the same.

Here the extension I did:

public static string GetCountryCode(this Country country)
{
    IDictionary<string, string> countryCodesInEu = new Dictionary<string, string>
        {
            {"Denmark", "DK"},
            {"Austria", "AT"},
            {"Belgium", "BG"},
            {"Cyprus", "CY"},
            {"Switzerland", "CZ"},
            {"Germany", "DE"},
            {"Estonia", "EE"},
            {"Spain", "ES"},
            {"Finland", "FI"},
            {"France", "FR"},
            {"United Kingdom", "GB"},
            {"Greece", "GR"},
            {"Hungary", "HU"},
            {"Ireland", "IE"},
            {"Italy", "IT"},
            {"Luxembourg", "LU"},
            {"Latvia", "LV"},
            {"Malta", "MT"},
            {"Netherlands", "NL"},
            {"Poland", "PL"},
            {"Portugal", "PT"},
            {"Romania", "RO"},
            {"Sweden", "SE"},
            {"Solvenia", "SI"},
            {"Solvakia", "SK"},
        };

    if (countryCodesInEu.Keys.Contains(country.Name))
        return countryCodesInEu[country.Name];

    return null;
}