The items you are looking for are called wire looms. They are made of plastic or nylon. The nylon ones are more expensive, but much more durable. The plastic ones will get brittle over time, especially around heat. Try doing a search at www.google.com for wire looms. You will find lots of places that sell them.

A wire harness is the wiring itself, if you ask for that you will not get what you are looking for.

Pat