Truck', the pros and cons of copper core wires have been described and debated in other threads, so it's not my intent to weigh in on that. But, good quality resistance wire does not stress the coil, FWIW.
To answer your question directly, many of the restoration suppliers like YnZ have copper core wires available, if "period-correct" is what you want. Many of the "usual" suppliers also have them, such as this:
Chevs of the 40s GM-stamped Spark Plug Wire Set.
Brillman is another good source that has options for both copper core and resistance core wire in sets that appear "correct" - select the style of wire and insulation from the drop down to see what options they have.
Brillman Spark Plug Wire Set with Options for Either Copper or Resistance Core Wire. A bit pricy. They have sets for other years... I selected '41-'54 just as an example.
Hope this helps!
Doug
