There are renders of the original trains that thomas and friends are based off of, not all of them, but they exist. The colours are obviously different, so it would require reworking these renders. You might have to ask nicely for these.
For maps, I believe there is a map of sodor on the maps website.
I don't think simutrans can offer this as an official release, but I don't think there is a problem with an individual making them for his/her own consumption. That basically means you make it yourself, for only yourself and no one else.