Does anything like a ScanGauge exist for us?

The higher-end scanners will let you read PIDs - the sensor values that the computer sees. Any scanner that reads OBD! systems and says it can read live data will tell you what you want to know. I have an Actron Autoxray scanner (I forget the model number), which does a good job. It can read the value of the ECT sensor, which is what the computer reads to determine coolant temperature. However, you'll be paying over $100 for one of these scanners; mine was about $250, and well worth it.

The ECT is the sensor in the metal heater tube on the passenger-side of the engine. However, the stock gauge displays the value of the CTS sensor, the small brass sensor in the lower intake manifold, just to the right (driver's side) of the distributor. The computer does not read that value, so no scanner will tell you what temperature it's reading. Which sensor is this temp gauge tied into? Knowing the ECT sensor value will help, even if you can't read the CTS value. You can at least see if the computer is reading the same value you're seeing in the temp gauge.