Weedwhacker said:
There are so many different types of milkweed, there must be some that grow in NC (I think?).
Unfortunately, the Monarchs are very rare in my yard for the past few years -- especially since the terrible winter of 2013/2014, despite having been plentiful prior to that. Oddly, though, an official "Monarch count" is done on the Stonington Peninsula up here, which is just across the Lake Michigan "bay of Green Bay" from where I am, and the numbers have been up the past couple of years. So, I keep planting more milkweed, in hopes that they will show up here again. 
Here's a field guide to Georgia milkweeds:
http://www.eealliance.org/asse...
I'm sure that most grow in NC.
I rarely see monarchs, my garden is kinda out of the route... The monarch that I saw this spring failed to visit the milkweeds.... Just nectared at the stokesia, and then left.
While common milkweed seed is readily available at Those "free seed" websites, it doesn't grow well in my sand.... The asclepias tuberosa is better choice, and the seeds are often up on those seed racks at the big box store.
Tropical milkweed is super easy, but there's a lot of controversy surrounding them... As being non-native... And possibly keeping the butterflies here past the appropriate fly away date... As well as concerns about butterfly pests.
After growing the easy milkweeds from seed, maybe you can experiment with the others... But matching the ideal conditions may be difficult, some of them are real specific as to growing conditions.
