Chest Pressure Regulation

We use a very simple "feedback regulator" in our operations. It is all mechanical and works very well for our applications. I know there are electrical options to do this but I would like to stay in this simple mechanical mode for our machinery. My question is does anyone know of a manufacturer of an item similar to this one described below. The unit has two diaphragms. One side is energized with regulated air the other side senses the chest as it is pressurized. A port feeds through the unit with air to open a valve that starts the pressurizing of the chest. As the chest reaches the regulated pressure it starts closing the valve that is supplying the chest and if the chest loses pressure the valve will reopen keeping a constant pressure in the chest. See the diagram below. We can get these regulators from the equipment manufacturer but I would like to find other sources as