While it may be exceedingly hard to find an authentic Pirates 4 script until a bit after the Blu-ray/DVD release of same, you might be able to find something kicking around eBay in another month or two.
Various "screen cams" of the movie, shot in theaters around the world should start appearing in the next few weeks online. While the quality would be horrible if you wanted to re-watch the whole film, you might be able to suss out what is being said.
Illegal rips of review DVDs, which often include subtitle tracks, may appear soon, or just a week or two before the authentic DVD release.
If all you're after is the last few lines of dialogue, you'd be better off searching Quora or the web in general for "what does Captain Jack Sparrow say at the end of Pirates of the Caribbean: On Stranger Tides?", and using the keen ears of a million fellow moviegoers to translate Johnny Depp's swashbuckled mumblings.