It might be awkward, but you could possibly build each product as configurable, and then the simple associated products could be the ones that are viewable in the various stores.
Probably not what you're after, but it could work with some elbow grease.
Aside from that, you'll need to set up multiple websites on the same installation. For that, start here: http://www.magentocommerce.com/blog/comments/video-creating-multiple-online-storefronts-part1/