lazy arm gauges

I am trying to locate a source (preferably in NJ) to buy a Lazy arm gauge. I think that is the proper name. It is a pressure gauge with a stop to hold the reading at the highest point that the gauge has read. We are trying to determine if the pressure on a job is going high enough overnight to cause the relief valve to drip. obviously we can't stay on the job 24/7 and watch the pressure gauge, so this kind of gauge would be just perfect. When we ask at the supply house, we get a blank stare like we are stupid. We may be, but I know the gauge does exist. Any help would be appreciated.