Comment 3 for bug 35374

The way most i2 connections are setup is that if you're on i2 and the destination is on i2, then the router will simply use i2, so to find a list of i2 Ubuntu mirrors one would simply compare the i2 member list to the Ubuntu mirror list.

Ubuntu Mirrors:
https://launchpad.net/ubuntu/+archivemirrors

Internet2 Members:
http://members.internet2.edu/university/universities.cfm

Small list of working i2 mirrors I tried:
Argonne National Laboratory
Duke University
Washington State University
Columbia University

A alternative method would be to look at the Gbps in the Ubuntu mirror list. If it's around 100 there's a good chance it has a i2 connection. Hope that helps!