You can always have an aftermarket tachometer sold in many car parts stores. However, these are additional units you have to place somewhere on the dashboard; not a nice thing to do if you want to keep the looks of your car as original as you can. But if you replace your instrument panel unit with one having a tachometer, you can have the same layout BXs with higher trim levels originally had.
You should start the troubleshooting at the sensor in the engine. Use a voltmeter in AC measurement position and observe the voltage at the two terminals of the sensor as you rev the engine up (have either an assistant or a long meter probe). If you measure absolutely nothing, the sensor is suspect (although you can check it with an oscilloscope if you can find one somewhere).