From what I could tell at the time, Lorraine's "Anime Hassin" snail-mail zine was ground zero for U.S. tape trading that wasn't associated with a university clue. (I'm forgetting her last name at the moment.) Each issue contained fan art and reviews, but for your yearly membership fee you'd also get access to tape lists for members from all over the country. My oddest and most obscure stuff came via Anime Hassin, and I've probably still got old issues squirreled away somewhere. :P