Having a 3G connection might help, but again, only if the thief doesn't restore the iPad, and there's no way to prevent someone from doing that.
not sure how to determine the IMEI.
There is no IMEI in a WiFi-only iPad. If you do have a 3G iPad and you ever synched it with your computer, Launch iTunes, go to the Preferences, select Devices, and hover your cursor over the backup file for the iPod. That should show you the IMEI.
I might just go to the Apple store.
The Apple Store will not be able to help you. They don't keep records of stolen items either. Only if an authorized law enforcement agency were to contact Apple would Apple perhaps be able to provide any information or assistance.
Sorry, but there's no other way to track your iPad. You'll just have to hope you or the police get lucky.
Regards.