Garage Romijn in Renswoude, Netherlands is a great source for parts, it is a family company that restores old big Opels. His showroom consists of cars where mirrors on the floor show the underbodies gleaming condition. These cars are not for sale, they are merely there to show final results of their work. Cars in their actual garage that are worked on have soft blankets dressed on them to protect the paint, that's their level of work.
The son works for a freighting company that can also handle pretty large shipments abroad, so that should be a bonus for you. He's got truckloads of parts as well, so a set of GSI bumpers shouldn't be a big problem.
