I think I got it - but it is not very elegant.
First, I save the group as a vcard to my desktop.
Then I use this converter to save it as a cvs file.
Now I open the cvs file in Excel.
When I open it up it gives me options on how to treat the data. Since I see that the info in the cvs file is separated by colons, i do not select any of the presets, but instead use "other" and type in a colon (:).
When the excel file opens, all of the e-mail addresses are in the same column, so I just copied and
pasted that column to a new page, sorted the column in ascending
alphabetic order (this moves all of the blank rows to the bottom),
scanned through the list and deleted the few names that preceded the
e-mail addresses (e.g. First Last <FirstLast@email.com>), then removed
duplicates.
I can now save this excel file back as a .cvs file or text or whatever I need.
Thanks to Tony Lindsay for helping me on this - and my wife for suggesting the Excel angle.