Last year I acquired a clone that was labeled with different location information of the plants I already had. I was fortunate to get both clones to flower this year and I was able to pollinate some flowers with pollen from the others.
And now (ta-daaa) - D. hamiltonii seed:
Very few seed, and only from the flowers that were pollinated from the other plants. I may have waited too long to collect the seed but I've noticed that many of species that produce many offshoots seem to produce small seed amounts.