If you do need replacement (used) instruments, it might be worth contacting John Wyatt at Rising Sun Restorations in Tockwith, Yorkshire. He has helped me many times in the past with the supply of good used parts for items that are either unobtainable or too expensive to justify buying new old stock.
John was one of the original CB 750 restorers in the UK and wrote books on the bike. He was due to judge at David Silver's CB750 day, but apparently didn't make it through family illness.
I will have a contact number for him somewhere, if you can't track him down through the internet.