Hi Arron,
You would need something based around the Geo-IP database to block by country, and I am unaware of any firewall which can do this. My best advice would be to have a look at the IP's the attacks are coming from, trace back to the service provider, then check out the regional IP assignment organisation (ARIN for Indonesia?) for all of the ranges that the SP uses - you should be able to supernet the ranges ( x.x /16 for example).
This is a very heavy-handed approach to the problem - I suggest looking at your firewall config (you are at least running Chirpy's CSF aren't you?) and look at investing in a good hardware firewall if you havent already - The WatchGuard Core e-series come highly recommended

and you can even script apps like CSF to automatically blacklist an offending IP at the WG :D