How do international organizations collect statistics regarding a country? How do international organizations like IMF, WB, and CIA Fact Book collect statistics regarding a country's economic indicators? 

What is their primary source of information?
I don't know how CIA gets its information from other countries on their economic performance, but I can tell you that IMF and WB have residence representative offices in member countries. Central Banks, various ministries and other government agencies supply periodic performance records to these offices.