Check in the yellow pages or on the web for sawmills. If you can't find any that way ask someone in the tree cutting business where to find a good sawmill. There should be a number of them in the Nashville area.

OK you won't find any cheap cedar boards that wide, probably anywhere in Tennessee. I wish it wasn't so, I'd like lots of cheap cedar myself. Sawmills do however have lots of oak boards that wide, usually at least 8 ft or longer. An oak board cut to the full 2 inches will last several yrs, not as long as cedar, but you can replace one at a time if you use a stake in the corners so the boards aren't fastened to each other, just the stake.