BitNinja has a country blocklist function that will block all requests from the IP addresses that are in the blocklisted country. BitNinja will block all the incoming requests from the country and also all the outbound (to the blocklisted country) connections from your server.
Here you can add countries by just typing in the name of the country. There is no option to add all other countries except one. This is because BitNinja is not for blocking countries but for blocking malicious requests from all around the world.