Where to find cars with good bodies and bad engines?

I would say that the best places to find cars with good bodies would be those places that have a dry climate, are not subject to acid rainfall and do not use road salt to de-ice roads. If you were looking for places in the U.S. that would match those criteria, I would suggest southern Arizona and southern New Mexico.

Bad engines can be found anywhere there are people who don't make an effort to maintain whatever gasoline powered equipment they own.