Your probably going to have to order it in. You might look or ask at any local Homebrew Shops you might have in the area or within easy driving distance. I know there is a pretty comprehensive shop in Orlando I have ordered from before. I don't know what others there may be around you. Do a Google search with your area and see what comes up.
You might even check if there are any vinyards in the area. They might have Muscadines of their own and get other juices or grapes shipped to them. We have one one about eight miles from here but I haven't taken the time to visit.