The missing part is generally called a shutter aperture scale (also called an aperture scale or f-stop scale). On Copal shutters, these scales are lens-specific, because the marked f-stops depend on the lens design and focal length, not just the shutter size.

That means you usually can’t use just any Copal #0 scale and expect the markings to be correct. Replacements are available from some large-format parts suppliers and repair specialists, but they can be relatively expensive. A repair shop that works on large-format shutters may also be able to source or fit the correct scale for your lens.

Good places to check are large-format repair services and specialty parts sellers rather than general camera stores.