Does one have to been in grace to receive interior locutions? I understand these to be thoughts that come once one has turned their mind to truth and righteousness.
Authentic locutions are pure gifts of the spirit from God, and cannot be sought, earned, trained for, worked for, hoped for or expected.
God can grant such experiences anytime to anyone for His purposes. They can be gifts of actual grace, motivating a person further towards their own salvation, or for many other purposes, ultimately to advance His kingdom in some manner or another. From my understanding, they would certainly be more common for someone who earnestly seeks God, but, as triumphguy, said, they come totally at His discretion in any case.