Simon, the Aero 8 parts book for S2 onwards to 2016 gives the rear pads part number as MBS06614.
The two locating pins as MBS006621 and the spring as MBS06621.
I suspect these are just MMC part numbers, so may not be what you need.
If you haven't seen this useful parts book it can be accessed via mogparts.net Uncle Melvyn's parts site.
