Where can someone find a defibrillator?

Many public place. An external defibrillator can be found in many public places, thanks to recent studies showing that availability of these automated devices can be used by even untrained bystanders to save lives during a cardiac arrest. Airports usually have them displayed on a wall, as do many theaters, concert halls, etc. Restaurants may have one as well but you probably have to ask someone to go get it.
Internal device? . You can probably go online to the major manufacturers like st. Jude and medtronic and try to buy one. I usually just go to the storage room in the hospital to pick up mine. I suppose there are used ones in medical refuse sites but i doubt you would want one of those! external defibrillators are now kept at all large public venues like airports and concert halls.