Yes, indeed common cars like these would be most welcome.
Problem one is these scrap and mill gondolas only look realistic when heavily bruised, battered and weathered, with each car in many varations and states to make them look natural.
Problem two is the lading, this also needs to be varied and realistic. Beams, slabs and rolls of freshly rolled steel, machinery and vehicles of all kinds.
A serious challenge for any builder and given the lowly nature of these cars and industries, probably not a best selling commercial asset. People would rather spend their money on a nice and gleaming streamliner instead of a pack of rusty freight cars.
There is a small selection available, but not in eastern and mid western road names where these once mighty industries were located, the present Rust Belt.
Look here:
http://www.stephan-michael.de/railsim/freight.html for a small selection. Most of these cars were designed a few years back or converted from MSTS, so they may look a bit poor from close up. Given the current performance problems of highly detailed and high poly assets, yards full of loaded scrap gons and machinery flats will do your sim's FPS no good however desirable such a sight may be.