Most plastic wind instruments, like recorders for instance, are injection-molded using styrene-based thermoplastics. These are pretty benign once they've been cast. But none of the materials that I've cast in silicone rubber molds are things I'd really want to put in my mouth. Epoxy, polyester, and urethane resins can all have nasty smells associated with them. Polyurethanes are particularly toxic to work with. But there are food-grade MDI ester polyurethanes that are supposed to be non-toxic when fully cured. I have no idea what they sound like, though, when blown through.
Are you sure you wouldn't rather make these from wood, on a CNC lathe?
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