I'm pretty sure that, in the Forgotton Realms jewellers don't just make "generic black circle" jewellery, because they'd be lynched as Sharrans by outraged citizens.
I expect that folks are really very careful not to give offense or acidentally identify with a faith they aren't part of because in the Forgoton Realms gods are real and real arseholes about things like that!
I'm pretty sure that you don't have a source for that.
In fact, I'm also pretty sure that I can point to treasure in Forgotten Realms canon adventures that contain jewelry, things like rings and necklaces, fashioned from numerous black stones. And I'll guarantee some of them even stipulate round.
