There are no (zero) transgenetic (GMO) native plants of any kind, milkweed or otherwise. The only genetic modification of native plants is through tens of thousands of years of natural selection. This is why they do so well in their native environment and require less maintenance than cultivated plants. Nature has selected them over time to endure your local conditions.
The plants that we distribute through Monarch Watch's commercial nursery partners are grown from wild milkweed seed that people like you collected and sent to us, or they are purchased from native plant seed distributors. We label each collection with the source information, send the seed to the nursery, and they carefully trace each seed source so that the plants remain in their native habitats. This is truly a grass-roots effort to restore habitat to areas where milkweed has been removed.