You can get the same gauge at Autozone or Sears. I have the same one. It also lets you take a fuel sample, using the bleeder valve and the clear tubing.
Look at the fuel line going to the throttle body- you should see a black cap on a Shrader valve, which is just like a tire valve, on the hard fuel line (I did see that you didn't see one). Don't put the gauge on while it's running and if you put it on immediately after shutting it off, put a paper towel over the valve and release the pressure- gas will squirt out.
Where in the Midwest are you?