Evidently, the Nutjob who attemped to poison the President (not the Elvis Nutjob, but the Child Molester Nutjob) bought castor beans off of eBay to make the ricin, then ground 'em up in his coffee grinder.
This answers what has been a pressing question for me. Back in the day, I wrote some training for first responders that spelled out, essentially, terrorist methods for killing people. The Anarchist Cookbook was one of my resources. I remember thinking it was way too easy to make poison from green potatoes or castor beans.
Further research led me to this: the castor beans sold in the US no longer contain the chemical that turns into ricin. (I don't remember how I know that. I think the government might have told me. Shh.) At any rate, I imagine Nutjob ordered foreign castor beans and got around the genetic mutation we apply to our beans.
Recently, when Meredith's next door neighbors sliced trays of potatoes and let them sit outside, I speculated they might be using sunshine to increase solanine, the deadly compound in green potatoes. Meredith ignored me. No one has died next door. I tried to back myself up with a reference to The Anarchist Cookbook, which used to be very easy to find online, but I could no longer find it and I was a little hesitant to hunt for it.