HankDio
Yamadori
Good luck on your journey! To my knowledge there are scant few alternatives to grafting for p. parviflora as a species. Zuisho is the only genetic individual I am aware of that can propagate from cuttings and air-layer.Zuisho is one I don't have but I have many dwarfs. A have seeds to plant and have done well with other pines but I am looking for larger seedlings for grafting and alternate propagation methods for the JWP cultivars I do have.
The crux of any cultivar is that they are clones, and therefore much of their behavior as a genetic clone is widely known and somewhat predictable. Perhaps another approach depending on your timeline would be to plant many seeds (say, 100) and experiment with the most interesting individuals. Perhaps you could be the pioneer of the Penumbra cultivar.