"Negative Battery Cable", correct term or not, is certainly as much information as any parts guy worth half his wait in salt, should require. The term "lead" is also sometimes used for "cable", but that shouldn't make a difference to a parts guy.
It's too bad that the Nissan dealer was such a jerk. Do you have another dealership to go to, or are there other guys (or gals) at the dealer that might be more helpful? Fortunately, my city has 2 Nissan dealerships and both have excellent parts staff - - except that their parts are usually too expensive.
Just a thought, are you sure you need to replace your entire cable? Your local parts store should have after-market battery terminal clamps that you just clamp the cable into. Maybe you could just clean up the remaining cable, strip the ends and use one of these clamps.
Anyway, good luck with your search and let us know how it turns out.