12V LEGO train tracks splinter
While I can't speak of the handling of these parts, the possibility of receiving official replacement parts from TLG is surely zero. That leaves us only the second-hand market, which fortunately offers genuine LEGO replacement pieces, sometimes even in brand new condition. Note though, that even though the brittleness problem might stem from lots of play or improper storage (for example being stored assembled), if it is a property of the material being used for these parts, then other pieces made the same time of the same material will exhibit the same problems.