I think you are talking about the dish shaped parts that fit behind the handle, which tend to be known as door finishers. (Just to help if you are searching for them)
There are two kinds: the original MG Rover ones which are ulmost unobtainable now other than second hand. These are chromed plastic. The other kind is chromed brass and were produced by an owner and other owners bought from the batch.
Planning is an unnatural process, much better to just get on with things, that way failure comes as a complete surprise instead of being preceeded by a period of worry and doubt