Where can I find it? Or can anyone please update what's the countries that are currently has iAd coverage?
Update:
Seems like my original answer was a bit misleading. The list on https://iad.apple.com shows which countries there have been sent iAd requests from. The column labeled Impressions shows which countries that have actually received iAds (and where iAds are supported).
So the actual list of supported countries is a lot smaller. USA, UK, France, Germany, Italy, Spain and Japan are supported.
It might be worth to mention that I have seen stats showing that other countries have received iAds, e.g. Norway, but only with a fill rate of less than 1%. I'm a bit curious on how this may happen, so if anyone know why, please explain.
Original post: (NB! The following is not correct. I'll leave it as it is for reference.)
I could not find any complete official list, but I know the ads are served in at least the following 18 countries. There might be other countries that I don't know of too, where my app has not served any ads yet. I found this list by logging in to https://iad.apple.com.
First page:
Second page: