perhaps one can use the 3D printer to print the missing track. Or simply buy one brand new but it will cost you an arm and a leg. Another possible solution is put a track over the existing tracks. it may create clearance issue.
http://www.ebay.ca/itm/Auto-Railroad-Cro...SwLnBX9v~Y
http://www.ebay.ca/itm/Auto-Railroad-Cro...SwLnBX9v~Y