Is there such thing?
I have been to different playgrounds and play areas but the see-saws I saw have seats made from either plastic or metal. It is actually very hard and sometimes, sitting in it, specially when your playmate likes a bouncy see-saw makes it uncomfortable. That is why I make sure my girls do not make the see-saw bounce so that their bottoms and pelvic area will not hurt.
Maybe the see-saw makers here in our country should optimize foams that are suitable for outdoor like those they use for boat seating.