High Weirdness by Mail is the only SubGenius book that isn't actually about the Church of the SubGenius. Instead, it is about various kooks, cults, and conspiracy theories. It is by Rev. Ivan Stang. It was the inspiration for the the first SubGenius wiki, the High Weirdness Project. If you actually want a copy, you'll have to buy a used copy from someone else, because it's out of print.
On subgenius.com, you can find links to almost all the kooks mentioned in High Weirdness by Mail. Most of them are still around! Here is a video by YouTube SubGenius MetaBob where he reads from High Weirdness by Mail about Breatharians, showing off that he has both of the out-of-print SubGenius books, High Weirdness by Mail as well as Three-Fisted Tales of "Bob":