Part number 16. It's hard to tell from the picture but it has a tab to hold itself into the caliper itself and has 3 notches that hold the actual brake mechanism in place
I probably wouldn't want to take out the one part of a working caliper. I'd be willing to send you the entire caliper though. Cable is broken and pads are bad but you could pm if interested and try to work something out.
I can't seem to be able to pm you either. When I click you name theres no option to message you.
But I'd be willing to sell it for $50 which would include shipping.