[MrB (Simon)]

The cable I have seen used on the high end scopes is known as ribbon cable. This can be bought from electronic retailers like Altronics and Jaycar, bought online or salvaged from old computers (IDE and SCSI drive cables)
Most ribbon cable is grey, tho there is also Rainbow cable which is very pretty tho not what you want, I have never seen black so flocking would be wise.
It comes in different gauges, but most is pretty light gauge, meaning for high power items you will need to use many lines in parallel to carry any serious current.

I'm not sure you would be able to use it for running USB though, maybe it can be done for short lengths like spider vanes.
Using ribbon cable means all the lines are obviously in parallel, which is bad for high speed data. Usual practice with ribbon cable(like IDE cables for harddrives) is every second line is grounded in an attempt to reduce crosstalk between neighbouring data lines.