Doubt if you will find “Off the shelf” bits at a sensible price, or even if they are available.
This assumes that you know the manufacturer of the base that you have.
Parts for a Starrett cannot be guaranteed to fit a Moore and Wright, or any other maker.
Making the parts is going to involve quite a bit of turning (parallel, taper turning, knurling and cutting threads)
By the looks of it, you will also need to make a new adjusting screw for the fine adjustment.
The threads MIGHT be BA, if British made.
So you would need Taps and Dies, and the knowledge of how to use them, plus the Die Stock(s) and Tap wrench(es)
You need the parts (At least three and probably a spring) for the clamp for the column, and at least one clamp for the scriber.
Without a lathe, I think that you are going to struggle.
If you want to gain some experience of using a lathe, (Buying one, and some books on operation, is a good place to start) or find a local Model Engineering Club, join and throw yourself on the mercy of some kind member, to help you by making nthe parts, or supervising you while you do the work.
Whereabouts are you located?
I’ll hold off taking photographs until you are more certain of how you want to, or can, go about the project.
Howard