Chris - decanters are being made all the time, and feel sure yours are quite recent - apologies, my comments were perhaps inappropriate and I was really only implying that modern machine etched pieces weren't my cup of tea, although I like the plain one. However, I guess that ships decanters are a style/shape that is forever popular so never go out of production. I like C19 machine etched pieces - just because they're old I suppose.

So what are you going to do with these two - sell on ebay??
I see that some of the stopper circumferences mentioned would suggest matchstick thin stoppers

- but my own feeling is that even if you got a replacement stopper from the same factory there would still some wobble - which is why they are made to fit and given matching Nos. at the factory, so that they are a true pair. I suppose one advantage of modern plastic inserts is that they provide a good fit as the plastic is a bit forgiving.
Bought the lone stopper you see in the attached pic., from a charity shop yesterday - just struck me as an unusually long example at 5.5" - 140mm - does have a No. and is good quality - haven't a clue as to age. Diameter is something like 19.5mm midway up the stub.
regarding Pete's missing stopper - are there places you can go and get one adjusted to fit your decanter - even if not identical to the original?
Probably not cost effective I guess.