Hi, and welcome. We’d need to know the actual tune (jig) you plan to play to say with certainly what would work. But yes, in general a D whistle is commonly used to play G tunes, and traditional G tunes from the Irish wind repertoire will fit in the range of a D whistle. C naturals are played by either cross-fingering, or by half-holing the top hole. The lowest note is D (there’s no C foot).
As for the whistle … We’d need to know the setting: amplified or not, large venue or small, accompanied or not.
Clarke make 2 types of D (and C) whistle: the Original, and the Sweetone/Meg.
The Original is a single piece, and non-tunable. If you’re playing with accompaniment, that can be an issue. The tone is breathy with low backpressure, and not as loud or penetrating as some other whistles, which may be a problem in a larger venue.
The Sweetone/Meg is 2 piece, and can be tuned to a degree if you can move the head. The tone is clearer and a bit louder. Some are reported to have intonation issues. They’re available in black and natural colors, but stores sometimes have them only in garish primary colors.
Other non-local inexpensive and reliable choices available to you might be:
o A tweaked whistle from Jerry Freeman. His Mellow Dog or “GenDog” might be a good all-around choice. 2 day USPS priority shipping standard. Contact info in this thread: https://forums.chiffandfipple.com/t/cp-gendogs-for-sale-new-frankenwhistle-soundclips/67997/1
o A Dixon Trad D from someplace like Hobgoblin Music or Whistle & Drum.
o A Susato Kildare D whistle directly from Kelischek
You can ask for expedited shipping, and have them in 1 or 2 days. The Freeman and Susato are fairly loud and louder; the Dixon has a quieter voice. All are tunable.
Good luck!