Recently I was asked to make a site visible to visitors of only a certain country. There's several ways to do this, the easiest being to modify the .htaccess file for your site. I found a site which allows you to generate a list of IP ranges by country. From there, it is a simple matter of modifying or creating an .htaccess file to place in your site's root. To deny access from a certain IP range:
order allow,deny deny from 126.96.36.199/19 deny from .... allow from all
and to include from only a certain IP range:
order deny,allow deny from all allow from 188.8.131.52/19 allow from ....