Ah, I missed that part. My apologies. I think they should have more to buy, but having the ability to buy those which are obtained through means of leveling or beating something should not be available in any shop. The best method would be something like I saw on an MMO I played not long before this released, they had dyes that you could use for the 3 dye-able portions and once used you could apply it to any of the portions and switch through as desired. Just have to acquire the dye to use it. They could have select colors for sale, then have the more wanted ones such as white, black, silver, etc. only obtainable from raids or leveling reputation or something. Doubt it will ever come to such a thing though as they already have a setup to it.