The Blunderbuss skins costs 13,500 gold to buy so it may take a little while to save up for it.
Even more expensive versions are available for 27,000 gold if you really feel like splashing out but most (except the Scurvy Bilge Rat Blunderbuss) are locked until you reach rank 48 in the various Trade organisations.
*** At least this is what I assume, the achievements are not unlocking at the time of writing.