Hmm, I was thinking just use the cable, but if you can remove the sleeving, then that opens things up for you. You could use the shield as a ground channel. I think that is done in some stock cables. Or you can see if you can find a three or four channel wire. The only thing is that with true old wiring, often times the sleeve was bonded to the cable with wax.
Paracord, shoelaces, nylon rope, and anything else that has a separate core from the outer sheath is play for you. I am not sure about sources in New Zealand nor the ease of shipping from websites, but Amazon.com has paracord, as does ebay. To fit around a manufactured cable, you will most likely be dealing with 750 lb rated cord (by US standards), which is Type 4 in other nomenclature. As for the other stuff, you can poke around hardware or fabric stores to see if there are any cords or laces that you can use.
Are you looking for 3.5mm or 6.5mm ends? Below are some links to products at shops that I use, but I can't make any promises about shipping internationally.
These are audio industry standard stuff which should hold up to routine use:
This is a website in China that has some very interesting looking connectors for reasonable prices. Not authentic on some of the brands, but to be honest, the quality isn't all that bad (and some stuff is quite nice):
This should get you started and give you an idea of what to look for. Good luck!