Cold cab solutions

I live in a cold part of Canada. Over 40 years I have had Land Rovers from Ser I to my present 3 Series III 88's. They were and are all cold in winter. Other than higher thermostats, radiator muffs and insulation, has anyone found a good gas heater like the old Southwind or Grebbersprecher (Volkswagon) for sale anywhere? I would install the old Volkswagon type heater if I could find them but they seem to be no longer available. My present Ser III which is totally restored is so efficient it doesn't warm up at all. The large radiator designed for desert work cools the engine too much for temperatures in the -20 range.