A few ideas:
In MA
Deerfield Academy-wicked smart, Nick Blixt, a great runner is a senior there now, he's like 8:55 for 3000 I think.
Cushing Academy- Hey, sintayehu Taye is a sophomore right now and he is not going anywhere. If you want to train with the best, he's a 4:09/9:00 guy, so that's on option. I think his brother is only a junior as well
Northfield-as suggested above, a terrific place to run, but I believe they have had limited success the past few years. Frank Shorter went there though. They have great coaches I hear.
Phillips Exeter Academy-I think has one of the best distance programs right now in the new england prep school world.
Sorry I don't know more outside of new england, but, hey you could always go to Mission Prep in Cali and run with Jordan Hasay.