Alright you got me curiuous about this Bartholina plant, so I looked it up.
There was another plant forum talking about this, I don't know if you tried this lead already...but one the members said a nursery in the western part of South Africa has a nursery called Duckitt Nurseries that may sell Bartholina, and they may also have some unusual Disas for sale as well.
Here's the link, just scroll down:
Darling, West Coast, South Africa
Their contact info is all there.
Let me know how things go, I'm interested in some of their Disas, maybe Bartholina later.