MTH keeps producing ore cars every single year. They have made them in many railroads that did not have ore cars.
Four railroads that did have ore cars are
Duluth, Winnipeg & Pacific DWP
Elgin, Joliet & Eastern EJ&E second-hand from CN or DM&IR
Escanaba & Lake Superior
Lake Superior & Ishpeming.
You can put the more colorful Diesel Locomotive paint schemes on the ore cars if that will make them more attractive to operators and collectors.