I would get in their faces as much as possible- politely and cordially of course. The reality is they have lives and careers of their own, so if you don't go out of your way to make sure you're a priority, you won't be. Start by calling around, but if you don't hear anything back and no one offers you a time to come in, just go to the office all dressed up and ready to shadow. Chances are, they won't turn you away.