I owe you photos on this one, but I too have a collection of marbles all of which were found lying on the ground. Most of them emerged from the soil of my garden. This land was cattle pasture until 1885, then was farmed, mostly walnuts, until 1948. An elementary school was built on the block in 1925, next to the walnut grove. My house was built 1949. A former resident used to bury trash here and there, and I still find old rusty bits and many pieces of broken glass, sometimes something interesting. Not any/many beads that I can recall.

The marbles are all mid 20th century, I believe. I discovered the source of many of them one day while working among the vegetables. I heard the neighbor's teenage son lobbing small objects over the fence with a badminton racket, and the swoosh and click as they hit tree leaves and branches. Later I found several clean, fresh marbles lying in the dirt. Others of my garden marbles look older and more battered.

Some other marbles in my collection were found on the street or the park or while camping... the criteria is that there had to be found on the ground. I don't buy marbles generally, except for a really big hand made one I bought last week at a thrift store.