Someone on mopo recently wrote about Halloween posters, one sheets to be specific, or US one sheets to be more specific as there is a few different versions, seems one of the versions is often rolled, the other two never, or rarely. Some discussion on exactly what they are and why.
Anyway, for me, I'd probably go for a folded one.
This isn't like your screen prints where they are made to be sold, these are and were made to be used, there's nothing wrong with a poster from this era folded as that's how they were meant to be.
I know some people don't like folds, but I actually hate rolled posters, they are a pain in the arse to handle.
But regardless, good luck, you'll find one, take your time and it will come along, they aren't raining from the sky, but it's also not really "rare".