Yup, return if this was accidentally purchased, send to a recycling center if you can't. This is a dirt cheap, group-regulated unit that has no business ever powering a GPU that requires supplementary power.
You're out of options, then; the builder should have provided them. Modular power cables are not universal. You can frequently find replacements or aftermarket alternatives for common PSUs from Corsair or SeaSonic or other mainstream companies, but it's nearly impossible to find replacements for ones from an obscure off-brand. In any case, you don't want to be using this PSU with a GPU you care about anyway, so it was a pretty lousy option even if you had the cables.
If you had come here and asked about a larger brand of power supply maybe someone might know. Even those tends to be hard since the manufacture can change the connections on the power supply even on very similar models.
You only hope would be one of the third party power supply cable providers. These are the companies that make the fancy colored cables for people that want other than black cables. You would have to get very lucky that they spend the time to research a off brand like yours.
You technically can build your own cables. You can get molex plugs that will fit into power supply side and the side going to a video card is standardized. Since a PCIE connection only have 12 volt and ground pins it is easier to figure out than the ones going to say a sata port. You have to have the skills to use a voltage meter and to crimp wires to the molex connectors.
Your best option is likely to spend your money on a new power supply that comes with the cables.