The Internet Movie Database (IMDb) is a well-established and comprehensive source of information on movies, which was bought by Amazon a few years ago. Each movie has a unique IMDb "Title" identifier. For instance, Terry Gilliam's film "Brazil" is "0088846". This IMDb id# is useful because it refers to the film, not a specific product. For instance, in North America you can get Brazil on DVD in two versions, a Criterion 3-DVD package (Amazon ASIN 0780022181), and a regular release (Amazon ASIN 0783225903). In Britain of course, everything is PAL video and region 2 coded, so it will be a different product (Amazon UK ASIN B00008WQ62). If you could search by IMDb number, you could search for the IMDb "0088846" at all Amazon locales, and it would return whatever products were available (for amazon.com, the first two, for amazon.co.uk, the third, and probably something else for Japan).
It looks like Amazon already has IMDb id# links in its database for most of the DVD (and video) product. If you look at the bottom of the Brazil product page, you will see a link "For more information about Brazil, visit the Internet Movie Database (IMDb)". This links directly to the Brazil page there, and the link contains the IMDb id# as part of the URL. I notice that this is only on the US site pages, but hopefully the other locales still have the IMDb info in their databases.
Of course, a specific Amazon product might relate to more than one IMDb id# - it could be a box set of movies, or a single DVD that has more that one movie on it. For instance, there is a single DVD with three films by the acclaimed Canadian director Guy Maddin, (Amazon ASIN B00005Y725). If you look at the "For more information" section, it properly has three separate links to IMDb, one for each of the films on the DVD. This would seem to indicate that Amazon already has info available to relate an ASIN to the appropriate IMDb id#s, and hopefully it won't be too hard to index and allow to be searched the other way, to start with an IMDb id# and return a standard ProductNode of all matching products. Finding the equivalent product in another country would be as simple as changing the "locale" parameter; the IMDb id would remain the same.
Note that IMDb movie pages have a "Shop Amazon" box, which connects you to an Amazon page with VHS, DVD or CD products related to a particular movie, for the US, UK and German Amazon sites. These links redirect to Amazon search URLs for particular ASIN products. For instance, clicking on the US DVD link for Brazil redirects you to the following URL:
Note that the three "keywords" it is looking for are actually three ASINs. Presumably at some point the IMDb people have looked up "Brazil" on the three country sites, harvested the appropriate ASINs, and stored them. They then redirect to a search URL for those ASINs when you click through. I suspect the ASIN harvesting is only partly automated. For instance, as of April 16/2003, the IMDb page for the film "Far From Heaven" doesn't show DVD availability, even though the release date was April 1, and it is on the Amazon site. Also, they haven't got a link to the UK DVD for Brazil, even though it is at the Amazon.co.uk site. If Amazon had IMDb id# searches, the IMDb movie pages could have a simple search link for the IMDb id#. They would still have to have a periodic process to find out whether any actual product existed for the various media and country options, but that could be completely automated to load into their database.
Now, if IMDb would only add SOAP retrieval for its info... ;)