I haven't actually seen one of those but if you can't find one then try a long one and wind it round a pencil, or something similar, and warm it with a hair drier, but not too hot. Stick it in the fridge afterwards to cool down and then remove pencil. Not as good as purpose spiral wire but should be O.K. as it won't get the harder use of a phone cord. I have used that method in the past where I needed flexibility in a cable.
OnePlus 5T review: Hands-on