I have bought the same set before and was disappointed as you were. Biggest problem I faced was that when I inserted them into my front mount dist cap, you CANNOT get them back out with out pulling the brass contact off.
It pretty bad when you can't even remove the distributor as a whole and work on it on the bench. I'll never buy the cut-to-length again. Get a better set with copper cores and save yourself lots of headache.
In response to your actual question...I highly doubt you could buy off the shelf copper core wires for a 40s-50s 4 cyl at any local auto parts store. Law of supply and demand, little supply = little demand. Gonna have to order em.
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