I had some free time at work (happens often ever since I informed my boss I was leaving to pursue studies in the US lol), so I used NALP's directory of legal employers to find out how many employers which have recruited foreign LLMs in the past do on-campus interviews.
http://www.nalpdirectory.com/dledir_search_advanced.asp

Search criteria are as follows: all blank, except:
"Employer Type": all 4
"Organizations that hire": Foreign LL.Ms
And then one search per law school selected in the "Campus Interviews" menu.

Georgetown 111
Harvard 109
U Virginia 103
Columbia 100
NYU 100
Berkeley 96
U Penn 95
Stanford 91
Duke 90
U Michigan 85
U Chicago 80
Northwestern 73
Yale 72
Cornell 60

All law schools: 184.
T14: 159.

Figures increase dramatically when you select "Domestic LL.Ms" instead of foreign. For example, Georgetown's 111 becomes 286 and Yale 72 to 147.

Of course, this is strictly a QUANTITATIVE measure. And I wonder how accurate it is, i.e. an employer reported as "recruits foreign LL.M grads" may decide not to recruit any next year.

Unfortunately there is no reliable QUALITATIVE data (afaik) on foreign LL.M grads (such as % per law school of foreign LL.M grads who were offered a job in the US).


Unrelated, but somewhat noteworthy is this ranking which uses US News' data but only takes into account peer assessments, judge/lawyers assessments, GPA, and LSAT while omitting categories such as expenditures per student, library resources, employment figures at graduation and at 9 month which are unfortunately often manipulated by law schools.
http://www.top-law-schools.com/forums/viewtopic.php?f=1&t=69377

('10 USNWR rank) / rank / school / score:
(1) 1. Yale 100
(2) 2. Harvard 99.8
(3) 3. Stanford 98.6
(4) 4. Columbia 96.9
(6) 5. Chicago 96.4
(5) 6. NYU 95.3
(6) 7. UC-Berkeley 95.0
(9) 8. Michigan 94.0
(10) 9. Virginia 93.8
(8) 10. Penn 92.3
(10) 11. Duke 91.7
(13) 12. Cornell 91.1
(14) 13. Georgetown 90.9
(15) 14. Texas 89.6
(10) 14. Northwestern 89.6
(15) 16. UCLA 87.4
(17) 16. Vanderbilt 87.4
(18) 18. USC 83.7
(19) 19. WUSTL 83.4
(28) 20. George Washington 82.6

Good info! Thanks Hedek! :-)