I just bought a 10-pack of pre-made Molex-to-2-SATA cables on ebay, took them apart, and made some multi-SATA supply cables that fit my case exactly.

It was cheaper than buying the SATA connectors separately from the electronic parts sources I looked at.

Simply some wires terminated to the power supply and some IDC connectors would be wonderful. (And a big red warning label "If you put the connectors on backward, you will destroy your hard drive(s).")

I think the spacing in different cases is too variable to manufacture for. Not to mention needing a bit more slack to reach different-size drives like 2.5" and optical disc drives.