How can I add salt and get it to permeate throughout chocolate?
You can't. Salt is water-soluble, and chocolate is made out of starch suspended in fat, without water. You cannot dissolve the salt in the fat. 

Adding small amounts of a liquid in which the salt is dissolved will also not help, as it will curdle the chocolate. At least it will certainly happen with water. Alcohol can have some chance of working, as it dissolves both polar and nonpolar compounds, but you will need pure (96% medical) ethanol, not an alcoholic drink. I think this is quite impractical even if it works, but you may want to experiment with it. A commenter who has tried it notes that not even alcohol will work.

The closest you could do at home is to make a ganache with either cream (standard) or water, and dissolve the salt in the water phase before making it. The least amount you can have is 20% water (if using cream or another liquid, you have to adjust for its solid content so you end up with 20% water in total). This will give you a creamy ganache, and quite concentrated, but not a chocolate bar. 

The only other thing I can think of is to go the way you already did - retemper chocolate and adding salt while melted - but you will not have it dissolve. What you can change is to grind it into a fine powder first, so you don't feel the grains as much. But it will still be grains suspended in the chocolate, not salt dissolved throughout the chocolate.