Diesel fuel heater
These heaters are not plentiful. I got mine on ebay a couple years ago, not for a great price. The guy who sold the unit to me was a over the road driver and repaired these units. He is located in Canada where the units are very common. Look for a Canadian who will help or do a search for Canadian salvage places.
The used units usually need a little repair but all are repairable. Using the unit I found, it was necessary to change the coolant pump to a larger pump because of the distance to the rear of my 35ft bus. Frank