http://www.kansasnativeplantsociety.org/wfoy_2015.php I just heard this on 98.1 Toby Tobin show.
I'm sure there's other seed sellers but I found this one. -
http://store.underwoodgardens.com/mobile/Antelope-or-Spider-Milkweed-Asclepias-asperula/productinfo/F1166/#.VqOeBstMFAg
2015 Kansas Wildflower of the Year Spider Milkweed-big for Monarch butterflies