Search for watch inserts for woodworking or wood turning. You'll find a few specialists here and in the UK. Sounds like a 1.5 inch before the sizes went metric? You'll be able to fit a slightly smaller size, and just pop an elastic band around the insert piece to hold it.
Failing that, a 'proper' jeweller should be able to get one. There was a jeweller supplier I used to be able to get some sizes from years ago, but they don't seem to be doing them anymore.
Is that similar i wonder to the little Waterford Glass type ones? I have one here that came out of a Waterford Glass clock, seems to be roughly same size, maybe I can try measure more accurately! It has a gold coloured surround, now it's not going at the moment as I presume the battery is long dead but have no reason to believe it might not go with a new battery. Have you a pic of the one you need?
Is that similar i wonder to the little Waterford Glass type ones? I have one here that came out of a Waterford Glass clock, seems to be roughly same size, maybe I can try measure more accurately! It has a gold coloured surround, now it's not going at the moment as I presume the battery is long dead but have no reason to believe it might not go with a new battery. Have you a pic of the one you need?