You could try Ghent Audio, just message them if they don't have a USB C option on their site. Out of what they offer, stranded Mundorf Angelique wiring is really good in DC applications.
You can contact Dave at Zenwave.com He has made a DC cable for both my Plixir and Farad LPS that I use for my router which requires a USB-C connection for power. Farad and Plixir use the GX16-4 connector albeit the pin-out is different for the Farad and the Plixir LPS.