I found both braided and laid cable marketed as “picture hanging wire” in the US. The laid stuff was about 0.032 in diameter and made from carbon steel, sometimes galvanized and sometimes not. It was soft, and a little too big, but great for the late 70s.
I bought a bunch of 36-inch lengths of different laid ropes in small diameters from an industrial supplier. They look great and are damn near true scale down to the construction and number of wires and strands, but they are almost all made of drawn stainless steel wire. That makes them much stiffer than real cable would be in 1/35 (Young’s Modulus does not scale . . .) and kinda useless for a model. They’d be great for a cable under tension, I suppose.
The copper items from Eureka XXL are really the best. I wish I could find the product from an industrial supplier - anywhere - but preferably in the US. I can’t believe E-XXL gets their stuff custom made (those places usually want minimum orders measured in miles or kilometers), I just can’t find the right descriptor to get there.
KL