D whistle:
D, Bm, G, Em
Some tunes in Am, A, and F#m.

C whistle:
C, Am, F, Dm
Some tunes in G, Gm, and Em.

Eb whistle:
Eb, Cm, Ab, Fm
Some tunes in Bb, Bb minor, and Gm.

Note that G turns up on both the D and the C whistles. Try both if you have a G tune. Em turns up on both the D and C. Gm turns up on both the C and Eb. Find the one with the best fingering and the best range.

Spend some time trying things that shouldn't work according to all the rules.

JP