Is there a switch available to control power to a thermostat for 20A 240V electric baseboard heater?

There are two types of thermostats. One is a line voltage stat. This is in effect a switch and when turned to the off position the voltage is interrupted and the heater will not operate. The other type of stat is low voltage. There will be a relay in the baseboard heater that the thermostat is connected to. With this type if installation to turn the power completely off you will have to turn the breaker off that feeds the circuit.