Try to melt your iron leggings/grantlets/high boots/low boots brought from merchants/gathered from goblinite in stock menu which are mixed with tons of other XXcarpsXX then.
When this becomes a problem for me, I hollow out a huge chamber and make it a stockpile that only accepts the goblinite, then have it use zero bins. That way, I can just designate the whole pile for melting every so often and keep up the fires without spending hours tracking the goblinite down in lists.
As much as I love knowing that each sock has its own story and feelings, I never actually get around to assigning a squad standard-issue undergarments. If there was a button I could push that would turn all the +large rope reed sock+ and XXllama wool shirtXX into -narrow cloth suit of clothes- and *silk suit of clothes*, I would probably push it. I might even be okay making boots and gauntlets a single item, although that would hurt a bit in adventure mode.