You mentioned Barry Nelson in your original answer, and Christopher Cazenove is another that I have on my list.
I shall award you the win as the final name that I am looking for could be considered to be rather obscure. Bob Simmons is considered to be the first actor to portray James Bond in the official United Artists series of films, an accolade usually (incorrectly) given to Sean Connery. Simmons never spoke but appeared as James Bond in Dr No, From Russia with Love, and Goldfinger. He was the actor in the familiar opening title that shows Bond walking from right to left, from the point of view of a gun barrel.
This scene was re-shot with Connery in Thunderball, and from then on used the incumbent James Bond actor.
Well done, your floor.