I'm replaying Pokemon Moon and I'm trying to find a cutiefly with shield dust but they always have honey gather, which is useless.
Well, if you're asking about the rate at which you can find Shield Dust Cutiefly, it is 50%, so you just have to keep trying. So far I've not come across any source claiming that certain Routes have Honey Gather exclusive Cutiefly, so keep trying!
In most wild Pokémon encounters, the Pokémon's Ability will be one of its non-Hidden Abilities (each having an even chance of appearing if the species has two)
-Bulbapedia