This is a very poor way to define "national".
Using this standard (i.e., pure geographic distribution of graduates), we find that Notre Dame is more national than Columbia and NYU, which is clearly not the case.This
Leiter/Sullivan study is far closer, but even it fails to compensate for the fact that the 3 highest-ranked firms in NY and Chicago are worlds away from the highest-ranked firms in Seatle, Portland, and Richmond.
The calvin study is okay. I think the problem with this study, to which you allude, is that by adding an extra factor like limiting it to selective firms, it is an impure study which measures placement in top firms more than it measures actual national placement. If that puts Notre Dame at the top, so be it. At least we know what the actual data shows and how to weigh it given that Notre Dame grads are not THE most sought after in the country.
There was another study I found on this but can't find anymore. It was "covelli" or something, the guy who founded autoadmit. But, it was very similar to Leiter/Calvin and had Chicago at one or two.
It is hard to think of ways to account for desirability of location versus inability to place outside of location. The only way I can think of is to look at the firms that interview at the OCI and determine how much opportunity there is to actually place nationally instead of looking at just the end result based on preferences. If the firms interviewing at your school are all local, that is severely going to limit your ability to move across the nation. If your school has an 50 firms from SF, 80 hiring to LA, 100 hiring to NY, 50 to Chicago, and 20 to DAllas, then you have a school that really gives you nation-wide options. If you don't have that, I'd argue that you are will be limited by going there.
One would be tempted to argue that a lot of Dallas firms don't interview at UCLA because UCLA grads would almost never choose to go to Dallas, so it wouldn't be worth the firms time even if the firm would love a UCLA grad. So this wouldn't account for sheer reputational power. However, it would mean that it would be at least a LOT easier to go to Vanderbilt to get a texas job because 20 Dallas firms go to the OCI. That is still a significant consideration for someone unable/unwilling to attend a school in a certain location, but wants a school that will make it easiest to land a job there.
I don't know how to find a good OCI list for all the schools, though, which has been updated given the current economy, but there are the bare bones for this at LSN.