From my industry: Perhaps the purchase of chemicals for the manufacture of fireworks. It's surprisingly easy to order pounds and pounds of different oxidizers and fuels.
The one I need is highly controlled. I need to make my own strike anywhere matches since Uco quit, need red phosphorous, don't want to scrape it off of match strikers for hours, want a big ol' jar. Apparently it's also used to make "MeTh" so I can't buy it.