YouTuber 'Custom Trackmaster just started making them with molds and cast resin or something. He has 8 recent videos on them and there are several different types for different engines. Watch his videos for how to buy them as he says he no longer sells on Ebay. He also just did a video on purchasing the plastic gears you may be interested in.
https://www.youtube.com/channel/UCjgiP5S...D9g/videos
https://www.youtube.com/channel/UCjgiP5S...D9g/videos