its not as hard as you think to do this. you find the very highest quality of animal protein and fat you can.
i eat sardines and locally sourced raw butter. both are very healthy and relatively free of contaminants. sardines have nearly zero mercury and because they are just baby fish have next to no accumulated toxins in their fat tissues. they are easily the healthiest fish to eat in my opinion. also look for locally caught fish from lakes you know are clean, do some research.
i get my butter from an amish farmer who feeds his cattle nothing but organic grass and seaweed. very very healthy cows, best butter in the world. if you go to the weston price site you can find a directory to finding raw dairy products across the US. in fact my amish farmer may sell via the mail, but i cant be sure about that.
i also get fantastic eggs from that same farmer. so you have to look around and do some investigating, ask around at the local health coop. but i highly recommend the sardines. i got used to the taste really quickly and now actually crave them because my body does so great with them. they are high in omega 3, natural calcium (dont get the boneless kind, they have little calcium), vitamin D, and b 12.