If I wanted to buy sashimi grade wild Sockeye salmon, I would buy it either from Fujiya or Angel Seafoods. Those would be the two place I trust the most.
As Culverin & Hamtofu wrote, you need to have a damn sharp knife, and preferably one with a heavy, one sided blade to do a proper job. Kind of like the bottom 3 of my knives in the below photo.
