Which automatic float switch do I need for the Pacifichydrostar model #68387

It seems late for an answer, but what you need is ANY float switch that will switch 10 amperes current. That switch can be placed directly in the power line to the pump. Septic pump systems also commonly use such switches.

When the switch opens, the pressure tank will probably suck to near zero, and make an obnoxious belching sound. This is a good sign, as the tank fully empties. Then, it is probably freeze-safe, if that matters.