This kid happens to be the curator of the largest tropical collection of bonsai in the US, and I also work in a retail plant nursery. People would rather argue on forums than accept factual information, that's why I don't post often.
Hate to name drop, but do you know Rob Kempinski? Only reason I mention him is he has been my local go-to-guy for pine knowledge and happens to have received a lot of national merit. He is the most knowledgeable on pine species in Florida, in my opinion, and he is apart of my local bonsai club. I've worked with him on Slash, Sand and Black Pine at his home. He's one of the only guys I know that even has a Sand Pine in a bonsai pot. I also know of Rosemary Voelker having one, this photo being her tree.
Rob and I did not graft or air layer them, but we treat them the same as we treat Japanese Black Pine and other 2-flush pines. Techniques to layer and graft should be the same, because they are 2-flush and 2-needle pines. And like you said, anyone with little experience can graft with 90-100% success rate, so what makes you believe this is an newly discovered cultivar?
http://www.thenatives.net/The_Hermit/meet_Steve/meet_steve.html
http://www.thenatives.net/The_Hermi...-s_creations_2/Grafted_Pine_Explanation_2.jpg
I said, dwarf sand pines grown on their own roots are not often found, but not unavailable. Witches Broom appears from either fungal, viral, bacterial attacks, or a genetic mutation. I do not think the Sand Pine witches broom is genetic because it is too common of an occurrence. The species must be prone to something that is causing the dwarfism. I wouldn't even be surprised if would revert back to the normal growth habit over time the same way Ficus benjimina 'Too Little' does.