Check shifter cart sprockets. There are several on ebay. If all else fails, I can dig through my old spares for one, but I haven't touched that stuff for almost ten years.
Wow, it isn't ideal but it isn't the drama so of you make it out to be. Like mentioned before, pitch is the same and the roller diameter is the same. A 415 FRONT sprocket might have been sexier just because it would have worn out pretty quickly.... EDIT:
The correct front sprocket costs about $15.00. It lasts approximately forever on an RS85. I always did my best to send my kid out on a well prepared bike.
Why not just throw the 415 on a lathe, just skim it a bit to make it as narrow as it needs to be and run a 415 chain? I’d have no issue doing that to a steel sprocket. Either way not a huge deal but something like that with my kid on it from a mental standpoint I’d want it to be right. Kind of splitting hairs but just the way I think.
Won’t hurt a thing to run it. I would just turn down the front sprocket though and run a 415 chain when I had the time.