I did finally find a POI (a walled house) with one stalk of Supercorn growing in the yard. I searched and found two more instances of the same POI on my map, but one of them did not have the Supercorn. I didn't think it was possible to randomize such things, so maybe it was a glitch when the world generated? I did end up getting enough corn to make a seed though
I swear I remember seeing Gracie at one point (in another POI), but couldn't find it again.
Thanks,
-Arch Necromancer Morloc 💀