Replacing Wall Electromechanical Thermostats with No Neutral Wire

Our (rented) office space is using a mix of cassette and standing HVAC units that are controlled via electro-mechanical wall-mounted thermostats, such as the Siemens RAB11.
They are simple units, with a heating/cooling switch, a rotating thermostat and a 3-speed ventilator control.
Looking at the wiring diagram I can see they don’t use a Neutral wire.
I’m looking for a replacement unit that would allow for local (as in not Cloud) control and automation, but I’m only finding options that require a dedicated N-wire (obviously to power the unit itself).
I don’t have the option of re-wiring. Any ideas?