If you need four of a part and have one, a mould is the answer. The reusable compound here needs no mixing or measuring: drop the bars into hot water until they soften, press the master into the warm material and let it cool, and you have a flexible mould ready to be filled. When you are done the same bars go back into hot water and become something else, which makes this a practical way to copy a hatch or a sculpted fitting.
Press the master in firmly but evenly, and choose a part with no deep undercuts — a flexible mould will release a lot, but not a shape that locks in. Fill with a two-part material from epoxy putty for solid small parts, pressing it into the cavity in stages so no air is trapped, and trim the result with steel sculpting tools once it has cured. Cast parts used for groundwork, walls and rubble fit naturally alongside the diorama accessories range.