I am interested in knowing on which international television stations
certain US television shows are broadcast - eg. Which Italian station
broadcasts "The OC", or which Mexican station broadcasts "ER" etc... I
would need to know this for most of the big US television productions
and for as many countries as possible. What is the easiest way of
tracking down this information?

I'm not sure if this is would be an easy way, but tvzap.com carries
international tv listings. You would have to browse through them.

I hope this helps.

Have a good day.