Any decent cocktail bar should have it, and should be able to make you an Aperol spritz.
We always have some Aperol around, and go through it pretty regularly. You can use it in place of Campari for a lot of Negroni variations - Longman's Negroni di Aquila is probably the most well known example, but even a traditional Negroni made with Aperol (and a good dash of bitters added) is great. I also use it in place of Campari in Boulevardiers (again with a healthy dash of citrus based bitters). Lately I've been putting a splash of Aperol into Weiss beers, good stuff.