I took a look through the mod tools and the closest thing I saw was a list of referral sites, which identify only the middle-man and not the user. As far as I know, external websites such as Quantcast only count visits and don't keep track of where visitors are connecting from. Thus, I think the only way to get such information would be to get a dev or other Stack Exchange employee to take a look at their logs, which I think is ethically, legally, and technically infeasible. I don't even know if they actually log the source of every visit.
So, I guess your only recourse is to ask Jon Ericson (or another community manager) and/or the Pope himself.