anyone know if i can get rear calliper adjustment mechanism?

Up until today I have been successfully refurbing the front and rear callipers, but upon trying to put the back ones back together I have broken the adjustment mechanism that sits inside the piston and the circlip too :-(. Does anyone know where i can get one? Or maybe has an old calliper i could buy? I've tried brakeparts.co.uk and ebay but no joy so far...
Thanks for any help.