Ceiling junction box

My son is moving into a new house that is 60 years old. He wants to replace fluorescent light in kitchen with new fixture. When we dropped old fixture we noticed the junction box is deeper in ceiling because of an additional piece of drywall on ceiling. So the box is not flush on ceiling and cannot hang new fixture. I read that they have extenders, is this something that will work? If so, are they available in stores and is that the correct name for it. Sorry so long... any help is appreciated. Thanks

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