I managed to find this wonderful foam-backed vinyl on E-bay, and I've used to trim several areas of the interior. It is dark brown with cream printed/embossed 'hessian' pattern. I believe it came originally from a well-known speed boat maker (probably commissioned for a specific model) and is no longer available.

These photos show the B pillars, where it was glued on and tucked behind the pale grey ribbed piping (it has to be cut fairly accurately.

I also fitted two interior lamps from a later model DS. Originally, being an ID19 this car had only one of the earlier type rounded lamps (on which the lense had melted).

The RH photo also shows the cleaned roof rail trim and the new grey cloth headlining.

.