Hi Jules;
Good luck with this project. It sounds fun, and a Mk III is quite an oldie. Assuming you’re in the UK (or possibly France?), I can only think of Merlin Pete, and I’m not sure if he would sell existing parts or not. Maybe you can also have a look at Spitfire Spares website, http://spitfirespares.co.uk/home.html I see there are some V-drive related parts on his Powerplant pages, although they look rough. One fairly early type vacuum pump as well. I’ve never bought from him, but he did reply when I was looking around for the nuts that sit at the top of the 14 cylinder hold-down studs. That’s all I can think of other than US suppliers.
Got any pictures of the project? I’m always interested in seeing these things progress.
Cheers, Tom Kay, Canada.