Maybe AliExpress?
Personally I just visit the Big Box of Cables in my spare room.
I usually canibalis my older power cables where I can as well. Every one of my power supplies I have owned (except one of two) have been Corsair, each one has been fully modular as well which has been a plus.
Definitely a good place to start, you just need to be careful when doing this. Not all cables are made the same between brands or even within the same brand. I have not fried anything yet.
Doctor power by thermaltake is a good cable tester especially if not sure.
Used to go to monoprice but I’m not sure about their quality anymore.
I will give them a shot and see what I can find. Was really hoping to find if Corsair sells their current connectors separately but seems like it’s a no.
Startek is what I have been able to find with their sata extension cables, seems like it’s the closest to what molex makes/made. Will see if I can canabiliz their extensions for the connectors and caps.
Never had to hit buy an extra SATA power connecters but usually cablemod.com is my go-to, or AliExpress if I wanted something exotic like a C-shaped connector or something.
Dream Big Ray on etsy!
I got my PSU cables for a corsair SF750 to fit exactly in a Dan A4.
The dude is super easy to work with and usually responds quickly. Only downside is he’s in China so shipping is either slow or expensive.