Some canned sardines are already de-boned, and for most bone-in canned sardines, you can just halve each one length-wise and pull out the spine in one piece. The bones are also totally edible themselves, albeit off-puttingly crunchy to some people.
If you're looking for a specific type of salmon my understanding is that wild Alaskan salmon has very low levels of mercury and the fisheries are healthy. I'm not sure where you are but it's widely available in the United States.
Is there something in between?