First Aid Corps and buuuk.com have created an iPhone app that can help you find an AED. The company is working on their database. If you find your self in this situation ask someone to call 911, begin CPR and ask someone for an AED. If one is not immediately available use this app to locate one. Hopefully, an ambulance will be there faster than you having to drive and get one.
Here is a video demo: Video
The direct iTunes link: click here