Hi Belinda,
Try contacting Tim Le Gros at Titoki Nursery. They grow plants of Nelson and Marlborough, but I don't know whether they would have an eastern Marlborough form. As Peter says, it's really quite variable between different parts of the country (even within the space of 50km sometimes).
I think there might be a local nursery that sells eco-sourced plants in your area. It would be good to enquire with them if so.
Motukarara's also a good suggestion.