I have 3 electric baseboard heaters in an open concept living, room dining room and kitchen set-up each on its own circuit and wall thermostat. Is there a way of putting all three or at least two, on one thermostat? I have checked with an electrician and he said no.

You could have a thermostat control 3 separate Contactors, when energized they could control 3 heaters that are each on their own circuit.
If you want to do something like that come back. We could explain further, or Hkstroud could privide a diagram.

Please explain further. A diagram would be helpful.
Thanks

HK is good with the drawings, I have not had success yet.
You would need 3 2 pole contactors with 24 volt coils, A Low Voltage thermostat to handle the 24 volts, and when set to heat, it connects the Hot to the heat wire, usually white or "w". Low voltage thermostat, pull Line voltage wiring for control if able to pull through existing conduit.
Otherwise Low Voltage thermostat wiring is fine.
You will need a 240 volts to 24 Volts Transformer. Provide fuse.
Connect the secondary 24 volts to 1 wire of each contactor, the other transformer wire connects to thermostat, then from thermostat to the other wire of each contactor. Whe set to heat and at temperature 24 volts will be present at the 3 contactors.