Many thanks Keith! There's actually a section in my recent Osprey Masterclass book that covers simple casting, from making a master, to the mould and then casting copies. I couldn't find too much of use online, so just practised and practised. Although the initial outlay for RTV and resin isn't particularly cheap, the small size of the parts means that the material do last for quite some time. I also don't use any casting equipment (such as degassing chambers etc) other than cheap brushes, pipettes and cocktail sticks.
Osprey probably wouldn't be happy if I posted too many pics from the book (!) but here are a couple showing the sort of content in there.