http://www.geognos.com/geo/en/world-countries-API.html看起来不错。

我是上面Erik提到的API的作者-我愿意提供帮助。
如果您需要特定国家的国旗，只需请求即可：http://www.geognos.com/api/en/countries/flag/GR.png
为了获得所有世界国家的JSON格式输出，您必须向http://www.geognos.com/api/en/countries/info/all.json发出HTTP GET请求
您将收到一个答复，其中包含有关世界所有国家的信息。每个国家都有一个名为“SeqID”的字段。
所有垂直排列的旗帜的png图像提供在：http://www.geognos.com/media/flags/world-countries-flags-80X40.png和：http://www.geognos.com/media/flags/world-countries-flags-32X16.png。这些图像可以通过使用css子画面技术偏移垂直位置来作为图像子画面用于服务各个标志。可以通过使用“info”请求的“IdSeq”字段和图像尺寸来计算偏移值。这是显示大量标志的最有效方法。关于使用sprites的示例，您可以查看以下页面的源代码：http://www.geognos.com/api/en/countries/info/IT.html
如果你需要任何进一步的帮助，你可以和我联系。Happy coding：-）

此服务提供SVG中的标志。
https://restcountries.eu/rest/v2/all
您也可以搜索特定国家/地区（不区分大小写）。
https://restcountries.eu/rest/v2/name/ {name}
例如，如果你想搜索巴基斯坦，这应该是你的URL。
https://restcountries.eu/rest/v2/capital/pakistan
您将获得JSON Resonance作为回报

[{"name":"Pakistan","topLevelDomain":[".pk"],"alpha2Code":"PK","alpha3Code":"PAK","callingCodes":["92"],"capital":"Islamabad","altSpellings":["PK","Pākistān","Islamic Republic of Pakistan","Islāmī Jumhūriya'eh Pākistān"],"region":"Asia","subregion":"Southern Asia","population":194125062,"latlng":[30.0,70.0],"demonym":"Pakistani","area":881912.0,"gini":30.0,"timezones":["UTC+05:00"],"borders":["AFG","CHN","IND","IRN"],"nativeName":"Pakistan","numericCode":"586","currencies":[{"code":"PKR","name":"Pakistani rupee","symbol":"₨"}],"languages":[{"iso639_1":"en","iso639_2":"eng","name":"English","nativeName":"English"},{"iso639_1":"ur","iso639_2":"urd","name":"Urdu","nativeName":"اردو"}],"translations":{"de":"Pakistan","es":"Pakistán","fr":"Pakistan","ja":"パキスタン","it":"Pakistan","br":"Paquistão","pt":"Paquistão","nl":"Pakistan","hr":"Pakistan","fa":"پاکستان"},"flag":"https://restcountries.eu/data/pak.svg","regionalBlocs":[{"acronym":"SAARC","name":"South Asian Association for Regional Cooperation","otherAcronyms":[],"otherNames":[]}],"cioc":"PAK"}]

标志图像URL位于“标志”键中。
来源：https://restcountries.eu/