I would think you should be able to find a frost plug heater.
Other options are lower radiator hose heaters or coolant cirulation heaters. Normally the coolant circulation heater would go in the cabin heater line. Last option is a glue on sump pad heater.
What country are you in?? If North america, look at the Zerostart catalog, http://www.zerostart.com/pub_AppGuides.asp If Canada, I have a lower rad heater you can have for mail cost, though it is probably cheaper/easier to go to a store.