All of my trees have been via mail order, and some are pretty large now. Finding local cultivars can be difficult. Trees can establish and grow fairly quickly, in fact. I hope someone suggests a great nursery, but in my area--north of NYC--larger collectible Japanese maples--if you can find them--cost as much as fancy jewelry. I think the West Coast people are the only ones to find the bargains. Home Depot has maples at good prices, but be careful of labeling.

Several of the Pikes Nurseries around Atlanta have a good selection of cultivars. Especially in the spring.

The Pottery in Commerce has a nice nursery with 30 or more cultivars.

I have bought several from GardenWright Nurseries in Cumming, Ga. They have over 60 varieties.
http://www.gardenwrightnurseries.com/

Mike