Could it have been present in the accessories of the natives of this time? Were there even mammoths in the Baltic region at the time? Could it have been introduced by someone?
This is less of a history question and more of a bio question.
In short, there were relict mammoths on Wrangel Island during that time period - but that's about it. Obviously, this is some way from the Baltic region...on the far side of Russia, in fact. So mammoth ivory would be quite unavailable, unless it were preserved in (rare) permafrost.
That said - there's a much more prevalent source of ivory in the Baltic region to this day. Walrus ivory, as well as the related material narwhal tooth, was available.