sawpalm, I would talk to your local Extension office and local nurseries. I know the rhodies that grow wild in the Appalachians are a lavender/purple color and using natives would probably achieve better results in the long run. I'd at least start there! Good luck.
Thanks for all the suggestions. Now, I'm going to start looking in the local nurseries. I know the Ext. Agent and that's a good idea too. I'm certainly aware of the Blue Ridge Parkway Rhododendrons ..would be interesting to see what the variety is. Not sure they are natives although they obsiously have taken hold there. I think Rhododendrons are all native to somewhere in Europe. Another fact to check out! There are native azaleas on the parkway which are orange and unbelievable. They bloom before the rhododendrons and the Kalmia.
Rhodendrons are native to many parts of the world, over 900 species, but concentrated in China, Japan, and eastern U.S. There are about a dozen native (N. America) rhododendron species (which now include both rhododendrons and azaleas), but the most common include Rhododendron arborescens (Sweet Azalea), R. calendulaceum (Flame Azalea), and R. catawbiense (Catawba Rhododendron). These are the ones that make such a brilliant show in the Alleghenies and Blue Ridge Mountains.
Your best bet would be the excellent cultivars of the Catawba rhodies as they are the ones that have been extensively bred with the most cultivars, most hardy in zones 4 to 8, and to -15º.
Rich, deep-purple cultivars include 'Anah Kruschke', 'Boursault', 'Lavender Queen', 'Lee's Best Purple', 'Lee's Dark Purple', 'Purple Lace', and 'Purple Splendor'. ('Lee's Dark Purple' will probably be the easiest to find, and very popular.)
Since you live in the Piedmont, your summers probably aren't as hot and humid as along the coast, right? As others have said, check local nurseries to see them in bloom which will help narrow your search to ones you like.
Many southern state's Extension offices have state or regional guides to the best rhodos and azaleas which will help you narrow your search.
Remember, good drainage is essential for survival. Balled-and-burlapped or container grown-plants are equally good to buy. If you do buy container-grown, be sure to "score" the roots vertically in three or four places along the outside of the container-shaped root mass as that will foster better root penetration that way.
The photo is of 'Lavender Lady', which is probably mislabeled from 'Lavender Queen'.