This is a general problem with a lot of these psychologically-scary-to-normies weapons, and also goes for a lot of hypothetical exotic cyberattacks with physical effects: it's usually much easier and cheaper to just lob explosives at something
It's a prescription medication, the amounts are diluted - you'd need hundreds of vials just to kill one person. It also makes a pretty poor weapon. The US and USSR both cancelled their botulinum programs in the 1960s because it was inferior in every way to nerve gasses and conventional explosives.