The Stellia use a fairly common type of connector, so you have a lot of options.
I'm not a cable naysayer, but after having bought some pretty high end cables for my headphones, I don't notice much difference in cables. I've had good luck buying headphone cables from Corpse Cables, Venus Audio, and C3 Audio. Places like Redco will make cables for you to your specifications. You can spend a lot more, but I think you get into the realm of diminishing returns pretty quickly when it comes to headphone cables.
How old are the headphones? Have you contacted Focal about getting a warranty replacement?