Ciao Jocelyn — Many state liquor stores have Aperol in stock, it’s best to call one near you and check to see if they have it or can get it. Many can order from the distributor and get within a few days.
If you want to buy Aperol online, you’ll need to do some investigation. Which State are you in? Each State has different liquor laws about who can buy alcoholic beverages online, specifically for the end consumers (thanks to the 21st Amendment), and that means where you live affects what you can buy online and from where.
Good luck and let us know if you’re able to find a place online.