If your search turns up nil, consider making what you need from Fimo modelling clay.

It shrinks a bit on drying, so form areas undersize on any key spots and then then carve them to the required final dimensional shape with an xacto knife, sanding block, etc. etc once it has cured for a few days.

I have used this for many camera modifiactions.

Key parts can be made black with the application of a sharpie pen.

It can be 'machined' to good tolerance.

Where it will be under tensile forces, I have sucessfully reinforced it by smearing hot melt glue over the affected section with a popsicle stick type disposable spatula.

Sorry I can help on the OEM 39mm tubes. I do have a set of surplus 42mm auto screw mount lens tubes.