Enter Monsieur Arban…
http://www.youtube.com/watch?v=8aE4RsecQKU
No reason why a whistler can’t pick up a standard woodwind exercise book or etude book and work through some of those tongue twisters. The whistle ìs, after all, a musical instrument just like a flute or clarinet or ophicleide and good musicianship is the same no matter what kind of horn we stick in our faces.
Another good exercise is to take tunes you already know and like to play and write them out in different keys – if the tune is in D, write it out in E or F# and play that on your D whistle! Good way to nail down all the “other” notes that will never appear if all your music is in D or G! Some tunes just “sound better” in C or E or B (to me anyway), and that just means if I want to play those tunes, I’ve got to play in four or five or no sharps. Not so hard.
Cheers