I just received my latest issue of Star Wars Insider (#92), and was surprised at what I saw in the StarWarsShop.com section. This section is usually dedicated to new and overpriced merchandise, but low and behold, they have a listing for Monkey Island 4!
Here is the online link:
http://shop.starwars.com/search/?keywords1=monkey+island&method=and&x=0&y=0)
Interesting, they're probably trying to get rid of old stock. Of course if they wanted to do that they should probably bundle it with the other 3 games.