The only place I've seen *real* jewelry is Mouseworks (I think - it's BIG and has gears in the name) at Epcot. It's along that path as you're going in - on the left. Or, when you're leaving on the right.
All the way in the front - or back - depending if you coming or going there is a nice glass-encased jewelry "store".
I also love the jewelry in "china" but it's not Mickey.