In this country, at least, that is something of a sub-specialty of a sub-specialty. In years of posting on these Forums I have rarely seen any meaningful discussion of Maerrklin trains.
I would start by seeking out members of the ETE (European Train Enthusiasts) which evidently has a Facebook and other forms of on-line presence. I know they have a Milwaukee chapter because they would set up a vintage Maerklin layout at Trainfest. It included vintage track as well as models, which of course ran beautifully.
Dave Nelson
Does anyone know how I can find out some values for a variety of items from the 1950's made by Marklin? Thank you.