Many of the independent nurseries in my area will take special orders for plants, provided that they already do business with the wholesale nursery that stocks the plant. (By "independent nursery," I mean a nursery that is not a chain.) So you can ask the wholesaler if it supplies any nurseries in your area.
http://www.baileynurseries.com/gcl
If not, you can call around to your local nurseries -- or go in person, with the photo of the plant you want -- and ask if they'd be willing to special-order for you.
Failing that, find a local garden writer and see if you can get them interested in the plant, write about it, and create demand locally.