Oh, I've read about this thing as well, but I haven't seen it in action either, much less a dump of it.
The weirdest thing is that this is not the only Metal Slug-related GBC pirate original with a 9/11 theme. There's also a version of BBD's Metal Slug 2001 with the same theme, titled
The Beet Terrif Battle of 2002 (sic, sic, sic!).
Edit: On a couple forums when I tried searching for stuff about it (and on the page you linked above, for that matter), I found out that Terrifying 9/11 is credited to a company named Hitek. They're also credited in a couple RPGs that have been dumped-- "Heroic Sword" and "Bokujou Monogatari 2", the latter of which is not Harvest Moon 2 at all but whose header claims that it is.