Only the highest ranking irons are likely to have access to him, so we'll have to make you into an overseer to find out what's going on in there.
I have a plan, for that, but we'll need some supplies.
Find one of the iron rune overseers at Dun Argol, to the southeast, kill him, and bring back his uniform.
Did you get the uniform?
This should work, but there's still the matter of the rest of your disguise. Even those dimwitted metal dwarves will recognize an impostor with a stolen suit.