Um, I've done some looking myself and I'm pretty sure that unless you preordered the LE, there's no way you'll be able to walk into a store and buy one.
It's going for around $100 - give or take a few bucks - on eBay right now, depending on whether or not the other preorder extra, the "Metal Gear Saga" disc, is included.
I wanted the movie too, but I'm probably just going to cut my losses and pick up the regular version when I hit Gamestop for MPH and Tetris today (selling back my old copy of MGS3 in the process, of course).
Also, one of the guys who posted a review on GameFAQs (so take it with a grain of salt) had this to say:
The Limited Edition bonus disc Existence is MGS3 recut as a movie. While the Metal Gear Solid series has been acclaimed as movie-like in it's presentation the idea of a MGS movie sounds great, on paper. But in execution, it leaves something to be desired. The "movie" is long. It tries to cram as much of the 15 hour game in as possible, and still make it entertaining. And it falls flat. The movie, just like the game takes it sweet time getting started and getting to the good stuff. There is a narrator that is prevalent from the beginning, then he disappears for a large chunk of the movie, then returns towards the end. The movie switches scenes around for what could be perceived as dramatic effect, but it makes the movie drag on for too long. The boss battles are 5 minute watch Snake jerk around with the in game camera then switch to the boss death scene. If you did not get the Limited Edition, you are not missing anything by having this.
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