The red "C" indicates "coated" and was dropped toward the end of the Nikon RF era (1956-57?) because all manufacturers were coating lens by then anyway, and there was no longer any point in advertising the fact that Nikkors were coated (Nikkors were always coated). Curious to know why you specifically want one without the red "C"?
🙂
I don't remember ever seeing one sans the red "C" personally, but there's one shown on this website (
link) so there must be more out there. They must make up a very small percentage of those 1,500 or so LTM lenses though.