If I'm not mistaken, Asclepias incarnata (Swamp Milkweed), Asclepias tuberosa (Butterfly Milkweed) and Asclepias syriaca (Common Milkweed) are the most commonly found Milkweed species in the U.S., which suggests to me that they adapt to a lot of different growing conditions, and also that they will be easier to find than some other species.
If you're looking for a local source for information or for plants, your state's Native Plant Society probably has a chapter in your area. I think most NPS chapter have spring and fall native plant sales as fundraisers, so that might be something to check out. Chapters in SC have monthly lectures and field trips except during the summer; NC probably has a similar system?
https://ncwildflower.org/
Good luck,
Virginia
