It's not that easy - scratches to lacquered finishes can be fixed up by simple furniture polish applied by 0000 superfine steel wool then polished with a fine clean cloth afterwards which is pretty straight-forward.
It's when the lacquer is gone you'll have problems. From memory Camcos stained their lacquer rather than the shells.
One way to get around that would be to match the stain (always difficult even if you're using the precise same Walnut stain they did at the time). Stain also gets darker the more often you apply it and often dries either darker or lighter than when you've applied them.
The lacquer used was nitro-cellulose which is not what is used now and, because it's so noxious, it's also been close to outlawed in much of the EU. Nitro doesn't like being put on top of existing nitro so you'd need to work out how apply the stained lacquer onto just the areas that need it.
Using old-fashioned shellac might be better - slightly shinier than nitro but much easier to work with on touch-ups like this.
Or you could just be lazy and apply bit of brown boot polish until you get something like the right colour, give it a quick buff and leave it at that.