Clackers, also known as Klackers, Knockers, Click-Clacks, Clappers, Clacker Balls and Ker-bangers, can be purchased online at places like Amazon, Party City, Etsy and eBay. Clackers come in a variety of forms: as two balls attached by a string, as two balls on a triangular frame with a handle and as noisemakers in a multitude of shapes and sizes.
Clackers originally became popular in the 1960s and '70s as two acrylic balls attached to one another on a string, allowing users to make a clacking sound when the balls knocked together. The balls would sometime shatter on impact with one another, resulting in a shipment of them being seized and the balls classified as a "mechanical hazard" in 1976.
The original Clackers from the 1960s can sometimes be found for sale on eBay, Etsy, or at TimeWarpToys.com. Some manufacturers have replicated the original design and offer reproductions for sale at these same sites. Make sure to check the year of manufacture if this is an issue.
Clackers that deviate from the original design are widely available online. The most common form is the Mini Clacker, which is smaller than the original and features two balls on a triangular frame with a handle. These are made of a lighter-weight plastic, which minimizes the chance of the balls shattering, but also lowers the device's noise-making capacity. Another common version is the Clapper, which reproduces the clacking noise by using two hands that clap together instead of two swinging balls.