This recommendation is from Bakery Manis, where you will find tons of great Hawaii dining suggestions for vegan and vegan-friendly. See personal details of her Maui listings here.
This gelateria does serve up dairy-based gelatos, but their sorbetto is vegan and dairy-free, and according to Bakery Manis, the selection is good, "lilikoi, lemon, raspberry, berry, guava, lychee, mango, etc." They also serve Maui grown coffee and espresso.
115D Hana Highway
815 Front Street
1280 South Kihei Rd. #101A