Try contacting Rhode Island Wiring. They will likely have those connectors and the sleeves that slide over them. I have used them for my '37 project and my '50 COE (complete harnesses) and the sleeves are not plastic but a firm rubber.
Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix