In 98% of cases "unaccustomed to" is used
unaccustomed to anything over 4.
He is unaccustomed to her accent.
I am unaccustomed to such delicate state.
unaccustomed to the clutch, the men would drive the hiccuping car away in the dust.
Overloaded, poorly maintained vehicles, unaccustomed to summer heat, can break down.
The book offers good, down-to-Earth advice that I imagine is helpful to men who are unaccustomed to childcare.
I'd sorry that you can't answer the charge because you're unaccustomed to dealing with different words at once.
I would not go there if you are unaccustomed to areas of financial impoverishment and are worried about safety.
unaccustomed to this outr ritual, but determined to do in Paris what the Parisians do, I started doing the same.
In 1% of cases "unaccustomed in" is used
The effect, of both these organisational and sporting triumphs, was a national good mood so unaccustomed in many it prompted suspicion and unease.