Clamp For Adjustable Height Perching Stool (PL4)

I'm in need of a single one of these things for an adjustment height perching stool it originally had all four but one has gone missing somehow.

I've seen these listed under multiple different names: C-type buckle, C-shape latch clamp, C-clip, E-clip, Push pin etc.

I'm in the PL4 Greenbank area and can travel a certain distance to collect if needed.

Thanks.