Thank you very much for pointing me to the right thread! I'll go with:
Find:
Code:
([A-Z])\. ([A-Z])\. ([A-Z])
Replace:
and replace "xA0" with the appropriate code for a nonbreaking space in Calibre.
That seems to suit me perfectly.
Since you asked, I just don't like line breaks after the first or second initial when I read a book on my Kindle.