Block access from countries to your site or network
You can find here the daily updated networkblocks for all the countries in the world. You can use them to block access to different countries you don't need or want to do business anyway. It is the first and best option to block if you don't want to spend much time looking at the masses of attacks coming from Turkye, Brasil, Argentine, Poland, .....
Do not forget to update your listings frequently.
At the other side, you should communicate clearly about this to your personnel and contacts on forehand.