Try MCM Electronics and also Allied Electronics. They sell a variety of K.O. punch kits and individuals for lots of applications, including DB connectors and "Double D" [the typical duplex receptacle has double D configuration].
Type in the respective company name, followed by .com into the URL locator of your browser. If you get lost in hyperspace, try your search engine with the company name[s].
I'll check a few contacts and let you know if they have more info.