Slingshots exist since the late 19th century. The very first models
were more of a sling-bow, but it didn't take long for them to develop
into the familiar Y-shape and shoot round projectiles from a leather
Slingshots were made by toy makers and arms manufacturers alike, in
operations ranging from cottage-style industry to large factories
employing modern means of mass production.
Compared to other collectibles, it is very difficult to source information about slingshots. This is partly due the little research that went into that field, but also due to the lack of official documentation (if compared to colletibles such as oldtimer vehicles, firearms, stamps, medals), and due to slingshots having been made in so many small workshops, which offered them locally or via mail-order for a few years and disappeared without a trace.
The German "AKAH" slingshot
British slingshots from the past