I made my own. I got a junk Ford type injector from my diesel pump shop and gutted it out. It is best to keep as much of the bottom end of the injector as possible, as any missing metal gives a false lower compression #. You need a pathway for free air flow, and a Schrader valve to allow the compression air to go to the gauge, but not back into the cylinder. I put the Schrader valve at the top of the injector (fine thread) and welded a air hose male end to the injector body. Look for a gauge with max pressure of 500 psi, fit it with small diam (1/4" max) hydraulic hose joined to an airline female disconnect.
Depending on the engine model (NA or Turbo) you can expect 400+ psi from a NA and about 375 psi from a turbo engine. My 401 6 cylinder engines still give these numbers with over 10,000 hours on them. When testing the engine, take out all the injectors so it cranks over very easy, and leave the fuel shut off cable in the "off" position.
Sorry, don't know how to post pictures.
Paul in MN