I don't know about the States but in Denmark you need an import permit and a phytosanitary certificate to import plants or seedlings from outside the European Union. It's very expensive even for private collectors.
I know Kesorn and adeniumseeds.com. He is indeed a friendly person and delivers very fresh and cheap seeds with a germination rate of 90-100%. I have ordered three-four times and every time the seeds arrived within a week!