SAE has a Boston-citywide chapter for all 4-year schools that don't already have an active SAE chapter. It's been done before in the city by non-NPHC groups (who don't have as much experience running a citywide chapter), so perhaps they will pick up some Harvard students as well or inspire other groups to do something similar.
I believe AEPi also does citywide groups in cities where there isn't one school with a critical mass of Jewish students large enough to support a healthy chapter on its own.
https://www.bostonsae.com/about-us.html