Bad news: still haven't found the leak. Good news: we were able to determine it wasn't from the house line, and we now have water back on. We still have no water out to the outside spigots, which means the bathroom in the shop still has no water, (because that's where it was expanded from), but the plumber will be working on a plan to modernize the outside section, and we'll be abandoning the old pipes to their rusty demise underground.