I've always found some great vintage pieces at Watchworks in Portland. You won't see them advertised on their website or on display in the store, but if you ask Alex (owner) to see his best Rolex pieces, he'll get them out of the safe and show them to clients he knows or has done business with in the past.
He almost always has old Subs (I've seen some with provenance back to Jacques Cousteau), 1655's, old Daytonas, etc.
www.watchworksPDX.com ... always ask for Alex