For the most part, the only place you will find surgical margin rates published is in medical journals. You are not likely to find on much websites, etc.
Other than that, yes, you pretty much need to go in for a consult and ask the question. Patrick Walsh suggests asking these questions and basically suggests that if they can't or won't answer them well, then that is a red flag. "Urologists who don't know their own results may not realize that their technique should be better".
Yes, Johns Hopkins is a medical school. The Brady Urology Institute
urology.jhu.edu/ there is nationally ranked #1 or #2 year-in and year-out. The first ever radical prostatectomy was performed there in 1904. Patrick Walsh, who ran the department for thirty years, invented the nerve-sparing prostatectomy in 1982 and dedicated his career to refining it. And Walsh built an extremely strong bench. Several of the doctors there have performed 2000+ prostatectomies. Their collective institutional positive surgical margin rate for organ-confined disease in over 10000 patients between 1993 and 2006 was a minuscule 1.8%.
There are some other excellent hospitals and surgeons out there but I think it would be hard to do better than Hopkins for this operation. I had a superb experience in all respects...