You mentioed "molex" which is the brand of connector and usually refers to the inside power cable as well. if that's the case, get your hands on a "Y-cable" and splice and dice as necessary. if it is something more different, look at these websites:
Get the part if available or something that has the part in order to slice it all together. For a neat job, you may want "shrink wrap" to insulate and pretty the job up.
The internal power cable in my external hard drive case is broken, and I have googled everywhere but can't find where to replace it. Anyone have a link for me to a place I can buy it online?