Where to Find Clickers
In Australia, Equilog
You can always try Target and WalMart in their party section, or any other type of Party store. If all else fails, start with the lid of a vacuum packed jar, a bell, whistle, a plastic bottle half filled with water (makes a distinct sound), a trigger snap, or tongue click.
And also try the regular pet stores. Some carry the clickers in the dog department.
You can use those plastic key snaps with the same coiled wrist band for 1.25 at Wal Mart. They make a nice click....enough to be heard across the arena. They are in the automotive section.
You can try what the dog people use and use an obnoxious ball point pen "clicker." (My farm collie also hates the standard clicker, but puts up with the pen.) Or you could use a whistle. Find something soft like one of a child's toy (although some of them are pretty obnoxious, too.)
Other alternatives: Snap of your fingers, sucking some air between your teeth for a special sound, the snap on a lead rope.