Hey Ginsu
The blanks/ coins are available on eBay, etsy, wish- places like that. My fav materials have got to be copper or jewellers gold.
Sink tube comes in brass and nickel plated brass, you can find that at any hardware store. Also check your area for plumbing/ industrial supply outlets. Places like that are everywhere, just harder to spot cause they don't advertise/ market for sales off the street- they work with contractors/ businesses and just bill them, but most will accept cash and walk ins, and even if they don't it's super easy to buy there. Just look at the work vans/ trucks that are parked out front as you walk in and at the check out just say that name... but just pay cash of course don't actually bill that company for your stuff lol. That's what I do at a few of my local places lol. Works like a charm lol.
A good plumbing/ steamfitting etc place will have TONS of diff pipe of all diff materials and sizes- just bring your hilt with you tho that helps big time.