I would think people would have enough common sense to search for and check the manufacturer's web page, if they have one, to start off with. That's sometimes not the case it seems. It might be helpful to include links for aftermarket suppliers as well.
Finding out how to order replacement parts isn't very hard...actually getting them, or even just getting the manufacturer to reply to messages is another story.
Anyway, for my contribution here's the support number for Tamiya USA: 949-362-2240. They're pretty good at customer service on the phone. Forget about sending them email inquiries, it's a waste of time - they've never answered any of mine. Just call them, and be prepared for a LONG wait (months) if they don't have the requested part(s) in stock and have to order from Japan.