Normally, when a steam-service Pressure Safety Valve is overhauled, it is immediatly tested, with steam, on a test bench, to verify the setpoint. That test, if done by a certified Test Shop, is sufficient.
I'm in the UK and I am currently on an inline testing contract, which consists of testing the pressure safety valves in there correct location. It gets very hot lol
rodbuster, go the National Board website and get the list of VR-certified ASME PRV test & repair facilities. Anybody that can test PSV's - subset of PRV's - specifically to protect ASME Sect I boilers, can steam-test relief talves. I'm sure that there is somebody just across the border from you. If you are going to ship them long-distance, there is an excellent shop in Louisville KY, just off Interstate 65 - Precision Services Inc.