Hawaii Native Milkweed

I'm so sorry.
No native milkweed for the state of Hawaii. There is milkweed present on the islands and the tropical monarch is on every island!

Hawaii does have the monarch, Danaus plexippus, which is amazing. I have see the monarchs on a few visits over the years. Danaus butterflies can repeat their life cycle of many plants in the apocynaceae family. The predominant plant currently observed on the Hawaiian islands is in the genus Calotropis. Calotropis procera and Calotropis gigantea have been growing in Hawaii for many decades.

Locals use the common name of Crown Flower for Calotropis gigantea. The flower has been used for lei source: digicoll.manoa.hawaii.edu/hawaiiflowers/Pages/viewimage.php?img=1769&famNum=2

C. gigantea is propogated by cuttings from an existing plant. Seldom produces viable seeds.
C. procera is propagated by seed which germinate easily. Frequently produces viable seeds.

I have seeds of C. procera grown in Kauai for sale in my store: www.growmilkweedplants.com/store/p59/procera.html
You could also pick them yourself from a nearby plant.

Calotropis gigantea is considered the "good neighbor" plant compared to Calotropis procera. That's because the latter spreads by seed in favorable conditions. Usually sandy dry areas are prone to seed dispersal colonizing an area. In addition to milkweed butterflies Hawaii has two native butterflies. The Koa Butterfly Udara blackburni #UdaraBlackburni and Kamehameha Butterfly Vanessa tameamea #VanessaTameamea. Host plants for the Koa are aalii Dodonaea viscosa #DodonaeaViscosa and dwarf koa Acacia koaia #AcaciaKoaia. Host plants for the Kamehameha is mamaki Pipturus albidus #PipturusAlbidus. There are other introduced butterflies like the Gulf Fritillary Agraulis vanillae #AgraulisVanillae butterfly I've seen it hosting on stinking passionflower species eg. Passiflora foetida #Passiflorafoetida.