I guess your looking for a modern radial. A few still offer a decent 14" selection but 50-Series I think is slim to none. For white letter, would have to be BFGoodrich's or the brands by TBC Corp (
http://www.tbcbrands.com/) through tire outlets which typically have a "Cosmetic Performance" line (many names, many labels).
Bias-Ply reproduction offers some other ranges.
Its' not easy. I've about given up on the Bias-Ply look as sizes are limited (most are too tall). Even 15" are limited selections. Trying to stay away from busy sidewalls too.
Paul