I always encourage people to email the manufacturer and ask for docs in such situations. It's the most proper place. If you do that and insist till you get an answer from their tech support, there are two scenarios:
you get the docs or hints about places to download them yourself. Sometimes you even get some wise advices for your specific issue for free from tech guys who have much more knowledge on the subject than you. Cool geeks work in support too, they will be helpful just because they won't see you as a buggy complaining customer, they will see you as a geek, just like they are.
you get dumped, which is bad both for you and for the manufacturer. Nowadays most people have blogs. It takes a couple of minutes to blog about this. In a moment your blog will get indexed by a search engine and the whole Internet will know that a certain manufacturer shall be trusted less due to their stance toward providing proper documentation to those who buy their products.