The correct three hole Borden connectors are not available today or I should say they’re not in production anymore. There are companies that sell three hole dental connectors today but the hole sizes are not the correct diameters as screen used Fetts.
Here’s a pic I saved from RafalFett (thanks Raf), showing correct hole size in relation to connector itself. I did buy two sets from the site listed as a test and the Large hole looks correct, but the second and the third holes are the same size and this is not movie accurate.
View attachment 71925
MojoFett or JodoKast89 are going to be your best options at this time