The traditional fabric is Ventile ( a processed cotton) and it can be purchased, maybe, at Point North in Britain.

Um, why on earth would you want a Scott tent? Are you making an antarctic base camp sometime soon? They are huge and cumbersome, and very specific purpose. The poles are like 12 feet long!! I've done a ton of repair work on them. I will try to remember the name the manufacturer who made the ones for the exploration company I did the work for,but I am currently drawing a blank.