If you're looking for models to add i would check out stuff from the Trainz Railroad simulator series. I'm pretty sure some of those models could be adapted to Farm Sim. I happen to know about quite a few models that would be suitable including ones you've been looking for Trainz Forge is a good website too look on for up #4014 and #844. They also have a couple of geared locomotives like a climax and shay. And under diesels Ive seen good F units.