12voltplanet will cut to length and have a vast array of colours incl with tracer.
All looms (as you’re probably aware) use a colour schema - its just a case of finding the right era for the colours to use (or copy the existing)
As an aside, Brother Needham sent me a link to a video of a guy rebuilding an Alfa Junior with a ferrari engine. For the recreation of the loom he used polypropylene rope to map out the routing in the car, taped on offshoots etc where the loom needed to split and labelled it all up. He then transferred it to a board, nailing junction points / transferring the labelling to make it! Simple really!