IP addresses don't neatly correspond to countries, so it's likely to be an imperfect match (i.e., you may fail to block some addresses in a country, or you may end up blocking some addresses that you don't want to). Google ip block by country for many sites listing IP address ranges. A couple of sites it returns: http://www.countryipblocks.net/ and http://www.blockacountry.com/. I haven't tried either of them and can't offer any endorsements.