how to add base region for other countries and how to group sites per base region


my first topic in WPMU!

I am trying to build a multisite network of independent sellers. Each seller is based on a country region, in my case a greek county.

First question: how can I add the capability of defining a base region when selecting Greece in the Location settings? similar to US or UK for example.

Second question: I am using the blog directory plugin in the home site for listing all sellers. How can I group sellers having the same base region?

Thank you