There's a few other exchanges where you might have better luck. There're exchanges for natives, seeds, and winter sowing. I've also gotten at least 5 natives from the plant swaps organized on this forum.

This year I've been saving some seeds to try winter sowing with. It sounds like winter sowing can produce many more plants from a given amount of seed. If you're interested I can let you have some seeds from Lobelia siphilitica (Blue Cardinal flower, Great blue lobelia) and/or Physostegia virginia (Obedient plant). I don't have that much of either, but can send you some for postage.