metal beads for pens in banks etc

anyone know where you can buy these beads / chains?
Im talking about the thing preventing people from nicking the pens.

any help would be much appreciated.

It’s called bead chain, or ball chain.

In the US most hardware stores stock it in the plumbing section; before ‘modern’ sinks with a levered stopper, it was used to connect a rubber sink stopper to the sink.