If you are picky it may be necessary to look through a few places.
You might look if there is some kind of writing on your moomin to indicate some manufacturer or a year or similar.
This could provide details for a search on ebay,
You may look on ebay for a few days then, and on an international search.
Well all in all its like house shoes. They are best when they are old but they fade one day.
So another possibility would be to look for a new one and break it in, make it used over time.
It may even be different from the other one but it may give a kind of similar feeling.
Maybe the feeling will be different but you may like it just as well.
hugs