Travel around the South around the time of the first fall freeze. Look for patches of just frost-killed kudzu and help yourself to the seedpods. It has such a bad rep that it would be hard to find the seeds for sale, but with a little scouting it isn't hard to find in unattended places.
There are several places in the area where I can collect all the kudzu I want during the season: behind the BigLots, behind the IGA, behind the Walmart, see the pattern here? Anyplace overgrown with kudzu will be some neglected property, and if the kudzu is happy and healthy (not too stressed by the kudzu bug), it will flower and set seeds. They look like
pea pods, and the seeds are about the size of a small lentil, 3-6 to a pod.