Hi Nigel, Mirrors are tricky to locate these days. The rubber gaiters deteriate and replacements near impossible to find. I watched a new one on E-Bay the other day which gives you some idea www.ebay.co.uk/itm/311870063218?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT But this one was advertised as Sunbeam Lotus which does boost the price. Later cars such as yours were fitted with Magnatex mirrors which I believe were unique to the Talbot range. I once heard that the mirror mechanisms were made by Hornby. Try Colin Hill, he might be able to help. Do you still have the rubber gaiter ?. What colour scheme is your Rapier ? I have an Alpine Rapier and two Solara Rapiers.
If you have the rubber gaiter then an internal mechanism and mirror glass should not be an issue to locate. Sounds like a very interesting project. There are two 'known' Blue and Silver Alpine Rapiers and both are/were for sale very recently. One of them is now on E-Bay, the other (B907LPF)is currently MOTed and road legal. Sounds very much like you have found a third survivor.