Someone has to make them. The terminals and weather pack seals are readily available from Packard electric.
Is
this the type of connector you are talking about? There are lot's of brands, Weather Pack is one brand, Deutsch, Amphenol, Metri-Pack, Amp Seal, Molex etc. There are lot's of different types of weather proof connectors. I have never even looked at the ones on the wolverine, but my guess would be a Delphi/Weather Pack.
Here is a basic kit you can buy.
Any more, I just splice and solder if I need to make a connection into the stock harness, but I have a lot of experience doing that, and wouldn't recommend it to the average joe. There was a time when I was making up sequential turn signal circuit boards for mustangs and selling them, but I don't have the time anymore.