@Hamotron I did a search and this came up–I think it will be a very helpful guide.
https://en.wikipedia.org/wiki/Orthodox_Jewish_student_groups_at_secular_universities
I think one of the things you need to contend with is that while the Orthodox community does go to secular schools, students tend to go to schools where other Orthodox students already go. And it is not necessarily schools that have typically large Jewish communities of other denominations. There is some overlap, of course, but just because a school is showing up on a Hillel list of schools with large Jewish populations, does not mean it is Orthodox.
I also second going to the Jewish B student thread. There may be some Orthodox students/parent son there.