The official Disney pin blog recently announced that one of the main pin centers at the Magic Kingdom will no longer be at the Uptown Jewelers. The pin center has been moved to the Magic Kingdom tip board area at the end of Main Street U.S.A. in between the hub and Casey's Corner.
Based on some of the pictures on the blog, it looks as if this new location will be more like a kiosk than a store. I have a feeling this means the new main pin center now will be at the Frontierland Trading Post. If you're looking for some of the more limited pins, Frontierland sounds like it's your best bet now.