I have been looking for this story since 1990.
A man goes about, dissatisfied by his man-made, mechanized life. He decides to try to find something real or natural. He goes as high up in the buildings as he can, but can only see buildings and sidewalks. He goes down into the basement, but can only find more floors down and metal stopping him from finding any earth.
Distraught, he finally decides to go for a walk and ends up in a beautiful park that he's never seen before. It is filled with green grass and flowers and birds and bees. He is overjoyed, until he realizes the bees are mechanical and so are the flowers, etc.
He has a meltdown and the ambulance is called. It arrives and the attendants turn off his switch; he himself was not "real" or "natural".
I found this in a sci-fi anthology.