[Gianluca Barbaro]

Thank you Jim, Alan.

I may add that, although it is aimed at two-handed playing, “Play melodica with both hands!” can be played with the right hand only, and you can play both staves (being the left hand “reversed”, it has the same fingerings of the right hand). And it definitely is a graded collection of exercises/pieces, being an adaptation of Beyer op. 101.
gl