Although they are custom, they aren't impossible to make even for the average joe. What makes them custom is the distance between the connectors and the special folding used to make the cable fit nicely. The cable is standard off the shelf stuff (metric pitch though) as are the connectors.
That being said, if you can get them from support for even US$20 it's probably just easier to get them from there.
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Christian
#40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)