In a search for vinyl material for the inside of our Beauford, we came across 2 companies that sell clear PVC rear screen material - someone was after this a few weeks ago.

These companies are as follows:

Automobile Trim
Classic Car Spares

The former could be trade only - they sell vinyl in 25m rolls, whereas the latter sells its Vyback flexible window sheeting in sheets of 50" by 40" at £18, 1/2 sheet at £9.50 and 1/4 sheet at £5.25.

Whilst this list is by no means exclusive, I hope this is of help.