Type "scrap" thats about as close as you can get scrap Buffers, Wheels, Bolier plates, bogeys and a bogey axle, and theres a "37 scrap loco it has no engine but you could edit and make one. Thats as far as i know good luck.
There is also an Awstralian diesel, a 45 or a 48, done as scrap.
A useful trick is to put down lengths of invisible track where you want the crashed vehicles and you can place any rollingstock you want on it. Of course this way the stock doesn't look damaged or broken but it is better than nothing. You can also lower the invisible track at one end (or both) and make it look like the vehicle is partially buried in the ground. Phil Skene set up quite a convincing looking derailment in his Urban Industrail 8a, the MoW session. Check it out for ideas.
You are correct, the mesh will not be there, you don't reskin with Gmax, the only thing a reskin would do is allow you to represent scratches, burns etc. To deform the mesh you need the gmax files. There may be some of the Auran vehicles on the source disk. Other than that, you could identify the owner of the vehicle mesh and ask if they would allow you to "crash" it. I know I am happy to give the meshes to others to allow them to modify vehicles if they ask.
Gmax is worth learning, although it is quite steep at the begining once you learn just a little you would be suprised how much fun it can be to have the power to build anything