I have 50 of the 18 pins cables custom made in stock, and also some 16 pins ones for early S5s.
12" long, they were like 1$ each. if I remember correctly.
There are/were for the S5 watercooled case, and some other projects, but it seems that they can serve other purposes.
Edit on availability and pictures
Anyone has the Digi-Key Part Number of the cable connectors?
I´ve been looking like crazy on this section without luck:
http://www.digikey.com/product-search/en/connectors-interconnectsI would love to build these cables myself.

I don't have the part number, but you'll probably end up paying more than the $1 I'm asking for each cable.
I'm making no profit on those cables.
To be transparent, I'm paying them $0.7 + shipping + 20% VAT on part and shipping.
I'm even probably at a loss if you add the time for packaging and actual packaging.