Mussels are not going to be a clean source. Mussels are filter feeders so they pick up a lot of garbage. The best sources for a lot of the EFAs you are looking for are marine sources though. So one option is to go with a fish oil but from as clean of a source as possible, which is cod liver oil. Otherwise you can go with non-marine sources such as spirulina and chlorella that will provide the arachidic acid as well as other fatty acids. Coconut oil will provide most of the other fatty acids you are seeking. The only one probably not covered would be the decosanoic acid.
I am not sure why you want decosanoic acid though. This fatty acid is associated with adrenoluekodystrophy and is believed to cause both arteriosclerosis and metabolic syndrome.