The Corsair Premium PSU Cables Pro-Kit Type 4 are compatible with the Corsair RM 750. These cable kits are specifically designed to work with Corsair RM series power supplies, including the RM 750 model.
The Corsair Premium PSU Cables Pro-Kit Type 4 are generally compatible with Corsair RM series power supplies, including the Corsair RM 750. These cable kits are designed to work with most Corsair RM power supplies, regardless of the specific variant of the RM 750 you own. However, it is always a good idea to check the specific connectors and compatibility of your power supply to ensure that all cables will fit.
Unfortunately we do not have a supplier where we can get the item you are looking for. The Type 5 kit has the manufacturer's number "CP-8920292", but it seems to be available only through Corsair.
Here are the details of the contents of the pack:
1 x 610mm ATX 24-pin
2 x 750mm EPS12V/ATX12V 4+4-pin
2 x 650mm PCIe Dual Connector 6+2-pin
2 x 650mm PCIe Single Connector 6+2-pin
2 x 750mm SATA
2 x 750mm Peripheral
1 x 24-slot
8 x 8-slot
You most likely won't find an adapter, you could get a pin-removal tool and painstakingly reconnect everything into the original Seasonic cables.
Phobya Molex Extractor Kit (Sleeving Tool)
Don't do that! Not all PSUs are the same and almost every manufacturer splices the cables in their own way. Even if it would be easier to use the cable set of the old PSU that is already in the PC, don't do it. You can destroy your PC components:
https://www.gamersnexus.net/guides/2702-psa-on-mixing-modular-psu-cables-dont-do-it
This also makes your question superfluous. This cable mod set was only manufactured for this one specific power supply unit and is therefore very unlikely to be compatible with others at all.
Extensions, on the other hand, are completely harmless. Here you do not plug a foreign cable set directly into the power supply unit, but only extend the original cable set.