The schools themselves have that information...but more importantly, why do you care?
When I was on the interview trail a lot of schools flaunted their boards rates as if they mattered...passing boards is not hard to do...some schools might make passing boards easier than others but with the P/F grading now straight numbers will tell you nothing.
Everyone I've met studied for boards the same way, Dental Decks, First Aid (type) books, and Old questions...none of which are provided by the school.
I would never consider board passing rate as a factor for choosing a school...its way more dependent on the individual.