They're not very common cables.Sorry if I'm being incredibly dense.... but surely you wouldn't even be able to plug the cable into the card as the 3x 8pin connectors would be female, but you'd need male connectors to plug in to the female connectors on the GPU?
Basically, you plug the 12VHPWR into the PSU as normal, which leaves you with the male 12VHPWR for your RTX graphics card.
You then plug the male 12VHPWR into a female 12VHPWR connector, the cable of which extends into the 8 pin PCI-E connectors, all of which are male for your graphics card with female 8 pin connectors.