There are three Code Making Panels (CMP) that deal with the issue. CMP 3 covers wiring methods in general, CMP 6 handles conductors in general and CMP 7 covers specific wiring methods.
I personally believe Jim Daly with General Cable would be a good first resource. He is fairly accessible and a member of two of the CMPs.
James M. Daly
General Cable
11 Valley Lane
Upper Saddle River, NJ 07458-1609