How to add a flag emoji to my iPhone's keyboard?

You can't add an emoji which doesn't exist. If there is no flag for your country, Unicode Consortium would need to create one, but a little research and I found this:

Somaliland doesn't have an ISO-3166 code, so no emoji can be created for it. A request for a code must come from your government. ISO is a standard published by the International Organization for Standardization that defines codes for the names of countries, dependent territories, special areas of geographical interest, and their principal subdivisions (e.g., provinces or states).

Further, Apple doesn't create Emoji. The Unicode Consortium does. But contacting them would be pointless until your country gets a ISO-3166 code, which you can't fix yourself.

It's highly unlikely you're going to see an Emoji flag for your country anytime soon, if ever.

Hello ~ In addition to *lobersterghost1* most excellent reply …try reading here…

https://www.iso.org/iso-3166-country-codes.html

It will not solve this issue but will give you more information.

~Katana-San~