So Cessna wants $1324 for a heating element? You may want to consider going the "owner produced part" route. The laws of electricity aren't any different just because its an aircraft part. There is a wire, or coil, that has a specified length and resistance, to produce a specified amount of heat at 28 volts dc input. These values may be obtained, and copied by the owner to produce his own replacement part.
Here's a good discussion on making your aircraft parts (or having them made for you, which is also legal):
https://aviation.stackexchange.com/q...aa-regulations
Reach out to this company about building one for you custom:
https://intekcorp.com/custom-heating-elements/
Finally, have you called all the airplane Junkyards? Off the top of my head: 1. Air Salvage of Dallas (ASOD) 2. Texas Air Salvage 3. White Industries Air Salvage 4. Dodson Air Salvage - There are many more smaller ones too.
#2 Texas Air Salvage has a 337 on their website currently being parted out:
https://www.texasairsalvage.com/Airc...php?editid1=34
Let us know how you solve the issue!