I have seldom seen many produce stands while on tour that others seem to never be far from. People often write about relying on them. I guess it just depends on where you tour and on what kind of roads.
While it might have been tough to buy one day quantities I prefer, some fresh produce would have often been enough of a treat to make me willing to carry more. Alas I recall only two times on the entire Trans America where we bought some fresh produce by the roadside other than in a store, once in a stand and once off of a truck. On other tours I remember similarly sparse pickings wrt produce stands. On the ST for example the only thing I remember was at either end there were some places selling mostly large boxes of citrus. These were common at either end, but the vast majority of the trip was brown sagebrush with not much in the way of towns let alone produce.
Perhaps there were more stands on some of my trips and I just don't remember some of them now, but they certainly weren't a daily occurrence on any of my tours. Many times it would have been a real treat to have some fresh fruits or vegetables.
I do remember that before I moved to Tallahassee I rode past two or three on just about any day ride where I headed out into the country from my suburban home (Maryland).