Check out answers 5, 9, 10, 14, 15, 20, 22 for names.
The West Coast isn’t very “preppy”, but look into McKenna, USC, URedlands, LMU, USan Diego (the private school, not the UC); kinda-sorta-for-the-PNW: UPortland to a certain extent, USeattle, Whitman, UPugetSound perhaps.