Three references which may help:
FAA AC43.13 - 1B has a section on flight control cables for airplanes. If it's good in the plane, it should be fine under the helicopter, inspect it the same way.
Loos and Company are a very large manufacturer of steel cable of all kinds, including aviation. They offer all sorts of refernce material.
Crosby is a manufacturer of cables and slings. Though not specifically for aviation, they have an excellent safety guide, which I would think has a reference to inspections.
I hope that helps,
Pilot DAR