Ask HN: where do I find newspaper circulation figures?

[loveatlonglast]

Where do I find the circulation figures for the top five newspapers in the top twenty countries?

For the past week I have been unsuccessfully searching for the circulation numbers on the top five newspapers in the G20. Circulation figures are tremendously important to the media industry. They are a principal determinant of advertising rates and last week there were many reports on the quarterly circulation figures falling for the top five US newspapers.

Are there any publically-available services that provide this kind of industry-level data? Would this kind of thing be an interesting counterpart to wikipedia, think a community-driven forrestor research?