GeoIP Country Lock is a perfect solution for you if you host country specific products. It eliminates the need to create multiple stores and provides a comprehensive management module. It lets you restrict access by blocking an online user, a country or a group based on their automatically detected IPs.
Create an Access control list and select the countries to whom access should be granted and there you go. Those countries which have been unchecked shall not be allowed access to your store and in that case you can set customizable message to them. You can also block immediately any online user with this extension. Another great feature this extension comes with is that you can specify a range of allowed IPs from within the range of Blocked IPs. Hence you can disallow a country as a whole but allow any specific IP to visit your store.
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