What you have are MAFAC Competition calipers. This transverse cable is NOT available anymore. I know because I was looking high and low for them a few weeks ago. Harris lists the part as unavailable... they even say (quoted directly from the webpage):

"MAF-4069 Compétition Transverse cable Gone forever, sorry! Don't bother asking!"

I did find a pair but they were with a caliper set on ebay that I was lucky enough to snag for $12.00. Here are two suggestions:

Search ebay for them either by looking for the cables themselves (they do pop up once in a while) or looking for complete competition brake sets. But be carefull because some Competition models (later years) take an entirely different cable!

Buy a set of MAFAC "Racer" brakes... cheap as hell... sometimes free, if you find an old bike with them. They use shifter cables for this part and are readily available when you need replacements.