Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I will second Gil's recommendations, but if you want to DIY then small pressure gauges in the 30 PSI range are available from multiple sources, like ebay:

https://www.ebay.com/itm/115385897140?

However, the problem being that you will need to make an adaptor to fit the Jensen threads!

I will add that you really don't NEED a pressure gauge, as your Safety Valve will actually be all the pressure indicator you really need, but I will also add that having a pressure gauge is sort of fun and does add another dimension to steaming up!!!