Ricin comes from castor beans as a byproduct of processing the beans. So it’s not hard to get a hold of, anyone can make it. But it’s not very subtle since it has a reputation. It’s not likely to sneak in under the radar when it comes to a potus, since they’d undoubtedly have preventative measures in place. Someone tried to send Obama ricin in the mail as well in the past, so they’ve certainly dealt with it before.