First off, thank you very much for the kind words. I'm am glad you joined the forum.
The "brown stuff" are in fact textured foam plates (roughly 37x13cm) which I bought from a train-modellism shop.
I know that the german company FALLER
makes them, but there are certainly many others that sell similar products.
If you really desperately need those plates, amazon.de has what you need
But I recommend you look for a train modellism shop near you, that will be cheaper
I hope that helps!