Hardware stores. It's a hit and miss thing, mothballs, Irish spring soap, dryer sheets. Come next spring you'll find the mice have been vigorously bowling with the mothballs and then wash themselves with the soap and dry off with the dryer sheets, chew them up and make nests.
Concentrated peppermint oil or oil of oregano do a better job. Another one is
Stay Away® Mouse Repellent
Stay Away® botanical rodent deterrent combines ease of use with biodegradable ingredients for a safe and environmentally friendly way to rid any home or farm of mice. The convenient pouches slowly release an odor that is offensive to mice and rats but pleasant to humans.
Rodents have terrible eyesight but a great sense of smell and they don’t want to nest in a place where they can’t smell danger coming.
Stay Away® comes in convenient pouches that you can use anywhere you have a mouse problem.
The best part? It’s environmentally friendly and safe to use! Unlike other types of rodent repellents or poisons, Stay Away® is safe for use around children and pets.
If you haven't had mice, there probably weren't any there in the first place.