Are there any Sephardi Poskim who Pasken like the Mishna Berurah that in a place where it is customary to expose the lower leg (with the knee covered by a skirt) that one need not wear socks or stockings?

I don't know of any. However you should note that the Mishna Brura didn’t write his Psak for Ashkenazim only, not every Halachic Psak of an Ashkenazi rabbi is only for Ashkenazim or of a Sephardi rabbi only for Sephardim.