One can allways buy a brand new unit. There are several sources: West Marine, Fisheries Supply, Amazon. One brand with a good record is the Force 10. You could also look at the Wallas brand of diesel stove tops. They double as a heater.
If I were looking for a unit, I would see what was available from boats that were being destroyed and parted off. Maybe E-Bay, but it would be better to go to a consignment shop at a boat yard.