Backman

21 hours ago, Dad3353 said:

A good source for much in the way of guitars is StewMac, who carry a very wide selection of spares and parts. Their site ...

StewMac ...

...lists 3-on-plate tuners of varying dimensions, clearly indicated; the ones linked above seem close. Prices vary, dictated by quality and production volume. You could try Yamaha themselves, directly; they may be able to help, although I suspect that, at the time of manufacture of your guitar, they were using pretty generic tuners anyway; nothing special.
It's also possible to remove the tuners and replace with individual ones, either by cutting away the missing one and replacing only that, or changing the whole lot for separate tuners. Obviously this could affect any 'historic' resale value the instrument could have, but it's an option.
Hope this helps. 

Thank you. You have give me food for thought. I will have to do more surfing.

21 hours ago, MWH said:

Hi Backman,    short of trawling the Internet,   no.   That's an old Yamaha,   could you find another and rob it for parts ?

Thank you. I might have to wait for the shops to open.

I have an old (circa 1956 appx) Yamaha dynamic guitar No.2, Nippon Gakki. Pat. No.48710Q - black label and I need new machine heads. One tuning gear and screw has been lost. The distance between post centres is 1 1/4 inches which is about 32mm. Any Ideas on where to get them?