How to block all email from a country code or other top level domain (TLD)
Add the TLD to the Local Bad Sender Domains. (Reputation -> Bad Senders -> Local Bad Sender Domains)
Use the format *.tld (with the * being a wildcard)
You can create a content filtering rule that will allow you more flexibility.
It will allow you to create exceptions to the rule or specify a policy group for the rule to apply.