Blocking spammers from certain countries requires expensive subscriptions to GeoIP database providers in order to lookup the IP country.
Have a look through the spam prevention page below for ways to block spammers:-
The best ways are to have email activation enabled, along with links and images disabled for the new member group. If you wish to go further you could also have moderator approval required for posts by members of the starting group.
If you also don't mind running beta versions, the 10.10 beta version available on the download page has built in support for StopForumSpam which is a database of known spammers which can block known spammers from signing up to your forum. The 10.10 beta version also has a new 'Spam Cleaner' tool for removing and blocking spammers that get through the other checks.