This is a folk-whistle or penny-whistle, and won't even cost a penny to download.
Versions included are sopranino in G, soprano in D, alto in G, and tenor in D (all versions are one octave higher than the corresponding singing voice).
The instruments are given as pieces. In ABS plastic they can be welded together using acetone. I have found this method to very reliably produce a functional and well sounding whistle.
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