If you are registering the car in Pa, you have 10 days to get insurance in place. If you are buying in PA but registering elsewhere, you can buy a transit tag at the time you do the title work to allow you to drive it back to your state and get your permanent tags/insurance in place.

I just went through this with my son 6 months ago.

As the others have said, you can do most insurance on line, once you find suitable coverage. Our agent issued a certificate as soon as we called him with the vin from the dealer. He is the one who told me we have 10 days.