You're kidding, right? There's a guy just outside her house that sells nothing but jewelery and gloves. Fat guy, I think he's called "Peddler." I believe she wants a silver amber ring, though that might not be all she'll accpet.
That's chapter 3, right? You can also find random "Merchants" in the Trade Quarter, in that busy place behind city hall and the bank. They sell rings and such. I'm not sure if Larivaldi (or whatever his name is) is still selling items in chapter 3, but he also carries rings.
No, you can't sleep with Shani again later. Don't worry, though, getting her Sex card or not has no impact on the rest of the game. She'll still be happy that you gave her Alvin. Just look up her card on the Witcher Wiki and move on. But it's really wierd that you cannot find ANY rings, anywhere? I'm usually selling them off by the handfuls each chapter, and anything you sell remains in the vendor's inventory for the rest of the chapter (maybe even the game).
Oh, I can find rings, but she's rejected all of them outrightly.
And I don't care/want sex cards. >_> My Witcher is one who would rather have money then girls (I get pretty deep into my RPG's if they're good.) I just thought that this would lead to me finding out more about Shani/my Witcher, which is always something I like to do.
/\/\||NG |\|O. Allian We lost. But we will return. Russia, World Cup Leaders, 2010.