I am a learner. The real experts on this forum are the two Johns - "Tiger" John Smith and "Grumpy" John Buxton - two fine and always helpful gentlemen who know more about guns than I ever will. That said, I enjoy learning about them, and your post has been a most interesting one as I did not know that the 14 bore survived into the autoloader era.
After your post, I asked around and found out that the only company that still makes shotguns for odd bore sizes like the 14 (though the big 8, 4 and 2 bores have recently been made as widely apart as the UK and Austria with Holland and Holland and Peter Hambrusch making them) is the great Italian gunmaker Piotti www.piotti.com
The website does not give much information but a very knowledgeable person told me that Piotti are the only company that make shotguns in virtually every conventional bore size ever introduced. Wealthy American and Arab clients fuel the trade, I guess.