Bristol 412 parts.

[Geoff Kingston]

I would try Bristol Cars first, not sure what they currently stock in terms of the instruments but they certainly had some of the switches as I got some replacements for my 603 from them.
If they can't help with the instruments try speedy cables in Abercave near Swansea they make new Smiths instruments and rebuild old ones and can offer new units where the old can't be repaired or are missing. They should be able to identify what you need and were very helpful when I needed to sort the water damaged instruments on my car. They also offer different coloured dials if you want to upgrade to the series 6 look of some of the recently rebuilt cars that have featured in the press.