There seems to be a European grower - somewhere - that sells these to nurseries and garden centers. I found a pretty large jack pine in Germany. Too bad it was a hundred bucks above my budget.
It seems that they are in fact available to the public in very, very limited amounts, a rare find.
I found a seller that's selling a lot of cultivars, but he has told me those are all grafted banksiana cultivars, which are grafted on regular banksiana. "Want anders wordt het niets". The ones (non-cultivars) in the garden centers don't seem grafted, but they're very hard to find and darn expensive. It seems you made a nice score with this one Storm87!
I'm resuming the hunt in spring.