Speaking as a former Napa employee, we had quality resources for rebuilding a host of parts, including water pumps. Because Napas normally deal in fleet-line and industrial applications, they have to have a network of qualified rebuilders available.I've had my local NAPA send many of my parts out to be rebuilt, water pump, calipers, master, etc.
There are a number of services like that listed in Hemmings Motor News. There is a guy in Michigan a friend has used and the business is just called Water Pump Man. He was happy with the service but I don't know the cost.