Article Link: http://help.truecommerce.com/en/articles/4537751-nexternal-find-customers-who-have-ordered-from-a-specific-category-during-a-specific-time-frame
This search can be done from within the Customers section. Go to Advanced Search/Sort in the upper right. Choose Order History Search. Choose an option for "Customers who have ordered a product in the category....." and "Customers who have ordered since (mm/dd/yyyy)". You can then export those customers or run a report on the results of that same search.