Here are a few possibilities:
* France (common definition of a country)
* Sudan (common definition of a country)
* Yemen (common definition of a country)
There are also some less commonly recognized countries or former countries with 6 letters, like:
* Tuvalu (an island nation in the Pacific)
* Malawi (a country in southeast Africa)
* Kuwait (a country in the Middle East)
* Guyana (a country in South America)
It depends on your specific criteria for what constitutes a "country"!