Anywhere - local or remote. Either thru infiniti or 3rd-party. Some have specific conditions that need to be met. Geico, for instance, has 15 months or <15k miles requirements, which can be renewed up to 100 or 120k miles.Can you do a warranty deal from any dealership and go to your local one or you have to go to the dealership you get the extended warranty from?
In our area, Carmax is offering 3rd-party extended warranty which is good and less hassle during claims from what I've heard. Unfortunately, they only offer it if the car was bought from them.