Finding a specific cable

IF you need flat, Goertz made nice sounding ones. For reasonably cost long cables, do what the pros do: balanced Mogami long interconnects. Keep speaker cables short.

Received wisdom is that for long runs you must use balanced ICs.

Still, also check out these:

https://audioenvy.com/product/speaker/sp12/

Balanced only pay benefits is noisy environments. Improperly done, they can be worse that unbalanced.