This may be lackadaisical, but you could figure out what KIND of police would enforce the "no-poaching" rules. For example, State Cops probably have the only authority on Interstates.
Call the local State Police barracks and ask THEM if it is OK to harvest seed pods or cuttings along a specific stretch of road, so you can propagate more of them. You might even say "and I'm going to re-plant 1/3rd of my sprouts in public places for the butterflies".
I'm guessing they won't care, and might say "no problem".
But they might say "You have to ask your lawyer, that's Not My Job!"
