Sooo just FYI: There is a page where they sell old german rolling stock, including contact informations. So if one would like to take pictures and probably some sounds from doors for example, this could be chance I think. https://www.db-gebrauchtzug.de/f?p=222:200:1104763932580:::::
DB gebrauchtzug only sells/rents trains to (real) train related companies. So I don't think they would accept a random company/people to use it for a train game
