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.
FYI: You can find a list of commercially available GMO plants here. Not all of the plants on the list are approved for market or cultivation. If you click on each item in the list you will see information about this, such as with wheat: "At present no cultivation of GM wheat. It is possible that it may enter the market in the medium term.”