Custom silver plated Thomas

There’s a process called vacuum metalizing that’s used to chrome plate plastic parts. I believe that’s what Mod Thana used for his custom and there are often companies who will do it for you. Here in the US at least, there were people who would do it to order for folks restoring old toys or plating model kit parts. I’m not sure who currently offers this service but it might be worth typing it in your preferred search engine.