Inlet manifold heater

Hello, I have a MK1 Jetta with a 1.5 carb engine.  I removed the inlet manifold and discovered something was rattling inside.

When I took the cover off the heater at the bottom, I discovered 4 round bits of metal with electrical contacts. ( I assume this is what heats up) anyway… all 4 metal discs where cracked and in bits.  Does anyone know where I can get the replacement parts … or what they they are called?

Thanks

Dan