If you don't live near a coast or a major city, the internet is your friend. Fish is flash-frozen and shipped on dry ice.
Unless it's explicitly labeled for sushi, "fresh" fish at a standard counter may not have been frozen to kill parasites. where to buy fresh fish for sushi
You’ll find specialized items like Bluefin fatty tuna (Otoro) or Hokkaido scallops. If you don't live near a coast or