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HA D3 recruiting picks up in late May and June, when the regular college season ends. Ivies are probably already mostly set, and, as TBP said, unless his velo is much higher that's not going to fly.
You have to have something to sell. What, exactly, have you said in the emails to coaches? You need to have better information to send than "was throwing 78-81 a year ago." It's not hard to measure pitching velocity, you should get it done. Is he playing for his high school? Starting on varsity? Doing well?
"the kind of kid coaches dream about - works hard, quiet leader, uber competitive, and is coachable" - well no, what they dream about is a kid like this who can perform successfully at their level of baseball.
Also, D3 baseball has no roster limits. There are all kinds of levels of D3 baseball, from schools where they will take as many players as want to go there, to the super-high-academic (HA) schools where admission rates are so low that the coach has to really want your son in order to help him in admissions. You have to figure out precisely which kinds of schools your son fits, between academics and baseball.