If your grocery store doesn’t sell salmon steaks, you can try requesting the cuts. We were able to order salmon steaks from the meat department and get them the next day.
You can test for doneness by seeing if the flesh flakes easily with a fork. Or, use an instant read thermometer inserted into the thickest portion of the salmon. The temperature should read 140F for medium and 145F for well done. Remember that salmon will continue to cook even after it has been removed from the pan. I typically pull mine out anywhere between 140F and let it rest for a couple of minutes.