Mine were 100% from plowed fields , and I always found more when I was barefooted lol , I moved to a new house on Chester river a few years ago and have been finding them on the shorelines at low tide. They can be harder to find with the backdrop of thousands of rocks but atleast they tend to be in great shape.
I like getting my feet wet myself its a challenge. I look in fields also though but mostly in the winter. Very nice ones. I find so many broken ones from the disc it makes my stomach turn.