Where can I find it? Or can anyone please update what\'s the countries that are currently has iAd coverage?
You can find the official list by logging into iTunes Connect and navigating to FAQ > iAd App Network.
The list of countries supported by iAd can be found in the answer for "What is the difference between the iAd Fill Rate and the Fill Rate?". As of June 2014, the answer states:
The iAd Fill Rate adjusts the number of total ad requests to reflect only those countries supported by the iAd App Network. These countries include Australia, Canada, France, Germany, Hong Kong, Ireland, Italy, Japan, Mexico, New Zealand, Spain, Taiwan, the United Kingdom and the United States.