[reiderM]

I'm looking for mating connectors for the rear traction motor output for the Model 3 packs (HV connector to rear motor).

Does anyone know the correct part number?

It looks like it may be Rosenberger, possibly HVR300 series HKK204-W20070B1-Y? Is there special tooling required to build cables with these connectors? If so, any ideas on a source to build a wire harness?

Have you looked on eBay? Most likely there's people selling these secondhand there.