As a kid, I could literally be running down the road (we used our feet to get to busstops in those days) and spot them. I had quite the collection in one of those peel-back style photo-albums. I also had a number of five-leaf, six-leaf, and one rather large eight-leaf clover. I rather assume it is a common occurence, because they always seem to be growing wherever I live. It probably helps that I have a preference for the “weeds” over the grass.
I seeded dutch white clover at my work, lots of 4 leafs in there!