In the comments, Martin said:

I wonder how accurate it is. Uncle Fester became underground famous in the 90s when he published books on meth and acid manufacture, but other clandestine chemists criticized his syntheses for being inaccurate.

From this small snippet, it sounds like he wants you to go out and find the right Clostridium species and strains in soil and culture them yourself, which sounds as impractical as his suggestion in the acid book to grow acres of ergot-infested rye. :)

Any more comments on why this is impractical? It sounds much simpler than growing acres of ergot-infested rye. He describes how he would isolate spores, first by heating the culture (this kills anything that is not a spore), then encouraging growth in an anoxic environment (kills anything that is not anaerobic). This leaves only anaerobic bacteria derived from spores.

The book does claim that botulinum germs are “fussy about what they like to grow in, its pH, and its temperature” and that “This need to exclude air from the environment where the germs are growing is the most difficult engineering challenge to the aspiring cultivator of Clostridia botulinum“, so he’s not saying that it’s a cakewalk.

Of course, many of these underground books (Anarchist Cookbook…) are rife with misinformation. Anyone serious about producing botulism toxin would need actual biochemical knowledge and multiple corroborating sources. Still, there’s a lot of information in this particular book that would at least provide a compelling starting point.

It’s worth noting that Uncle Fester probably never synthesized all the compounds described in his book, which includes over half a dozen different types of nerve gas. He repeatedly points out that synthesizing these chemicals is a risk to the life of the person performing the synthesis. In some parts of the book, he names sources, like literature released by the military, but the vast majority of his book lacks citations.