Rapid keep drag cable in various sizes at whatever length you need. When I say "keep", they actually order it from the German factory, hence the 7 day leadtime.

https://www.rapidonline.com/Catalogue/Search?Query=drag%20cable&Size=20&Attributes={%22N o.%20of%20Cores%22:[%224%22]}&Tier=Drag%20Chain%20Cable

Don't understand why you don't want to use 4 core for your 3 phase motor, simply leaving one core unused, or possibly use it as a ground.

For motor connections, you could also use an SY cable. The braid will provide protection and also some EMC screening. https://www.tlc-direct.co.uk/Main_In...BoCk4AQAvD_BwE