Thanks again for all the help, Chaddz3!
I did some more digging and I seem to be making some progress also.
I still have an E-mail to another Ford dealer, but I called Tousley Ford while I was waiting.
He found a fog light wire harness P/N of CV6Z15K867B - which lists for $14.32. He isn't sure it's the right one, but he showed one harness for "With Park Aid, With Fog lights" - which is probably the one I mentioned earlier, one for "With Park Aid, Without Fog Lights" - not sure what this would be on a Focus, unless the harness is used on other models, and the above for "Without Park Aid". It didn't say anything either way about fogs, but I think those are the only things those harnesses go to, so I assume it would be the fog portion of the harness, and the 15K867 center part of the number checks out.
The P/N of the BCM is BV6Z14A068LC and it lists for $222.23. He said it is the same part number for all 2013 SE's, so it probably supports fog lights, but he didn't know if it would need to be re-flashed. Not as expensive as I would have guessed from the comments in this thread and others.
Finally, the headlight switch is CM5Z11654 for a 2013 SE With Fogs and lists for $49.31 - which is odd b/c the 2012 switch was over $100 ...