Leading Edge’s awesome boardgame based on the movie Aliens had one official Expansion, and that was that. No more addons, official or semi-official… except one.
Published in “The General” Magazine, volume 32, issue 1, was a short article by Stuart K. Tucket that suggested some alternate rules and scenario variations for the boardgame.
While these were unofficial, they are the only published “addons” to the Aliens Boardgame that I know exists.
Since the magazine is long out of print (like the boardgame itself) and not easy to find, I am posting it here both as a cropped image and a full-page pdf scan, for those who want it.