This article is from the Beer and Other Brewing FAQ, by Kurt Swanson email@example.com with numerous contributions by others.
The wang archive server contains the file "suppliers" which is a good place
to start, or try the classifieds in any copy of Zymurgy. Also, try the
yellow pages under "Beer making supplies" and "Wine Making."
Lastly, the original copy of "the Cat's Meow" (see #5), contains a list
of mail order shops.