That would be the e-mail address for the article's author (whether or not it's still valid after all this time, someone else can test).
The URL for the article, however, is this:
http://www.lavasurfer.com/boxtop/boxtop-11.html
-- and while that 1999 page has not been updated, the website itself is still going strong and updated regularly:
http://www.lavasurfer.com/boxtop/boxtop-112.html
Unfortunately, the promised follow-up article(s) never appeared, as far as we can tell. There's only one related bit we can find in there, a reminiscence from the author providing no substantive information about the card sets:
http://www.lavasurfer.com/boxtop/boxtop-21.html