not sure this helps, but if someone has made the cars you want, just not in the right color, you might have some luck with reskinning if the texture mapping makes it easy. I've reskinned a few Trainz assets before using gimp- it can be done. Was a bit daunting at first, in some ways it still is. But the results can feel very rewarding- and who knows how long it would be before someone else does it.