Hetty, this is a breathtaking plant. First, congratulation on such a great find. I really would love to have a cutting if possible whenever you can, I can trade something or postage up to you. Hetty can you let me know the name of the Nursery? I will be in Sarasota, so may be I can visit it.
Now , my experience with rooting. I am not a very good “rooter”, but I really wanted one plant that is hard to root. So I did an experiment and Yep, I got it done: you can take perlite, turface , napa product or 50/50 soil and perlite. Plant a cutting , water it and put a pot into some container so the pot is kind of hanging. Put water into that container. The pot you planted your cutting in do not touch the water. You do not need to water your cutting constantly just from time to time and wait, wait , wait…… I rooted a desert rose using this method and I was never able to root a desert rose. You can try and see what happens.