It's very usual for 2nd readings to be done by one of the expert pathologists, so most doctors have no problem with it, and should suggest it as a prudent process.
In a good % of cases 2nd readings indicate a different result. Obviously this can have an influence on how agressively you might approach treatment options.
I'd just tell him you'd like the reassurance of obtaining a 2nd reading: it's unlikley anyone will object. If necessary, reinterate that you will feel more comfortable with the process once that's done: he'll go along with it, as you're the one paying the bill, and it's in everyone's interests.
Some of the pathologists who can provide the service are at Johns Hopkins Med School, University of Virginia Med School, Stanford University Med school.
A very good book on PC is "Prostate Cancer Prevention and Cure" by Lee Nelson MD. Although written a few years ago it's one of the most comprehensive books I've seen. It might not have the latest details on some of the newer treatments like robotic surgery or HIFU, but that information can be readily obtained here.