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Do you mean solid sheet material, or liquid resin? I thought you meant liquid.

You don't need special materials for making scales.
I usually use tropical hardwood. I've used bone as well.
I've...

I'd go to a hardware store. Not a halfords, but a decent store where professional carpenters / ironworkers / ... buy their stuff.
Or even a properly equipped DIY store. They should have a wide range...