Qmark has a new part # for their MUH series built-in thermostat. The MT-1 wqas replaced by the UHMT-1 and can be found here:
https://morelectricheating.com/default.aspx?page=item+detail&itemcode=QMARK685360152417
Qmark Marley Type MUH Series Unit Heater Accessory – Field Installed Single Pole Internal Thermostat (40-85F Temp. Range)