http://www.proxyfire.net/forum/showthread.php?t=33
ProxyFire does that, using Maxmid GeoIP :
BenyCode:http://www.proxyfire.net/forum/showthread.php?t=33
You could try this. http://www.maxmind.com/app/geoip_country I integrated it into my proxy program i coded.. It's pretty accurate enough for being free. They also have a paid version.