The following material is Open Game Content from a 3PP Source
Mithral Clockwork Familiar
You rebuild your clockwork familiar from mithral parts.
Prerequisite: Improved Clockwork Familiar; 500 gp worth of mithral.
Benefit: Your clockwork familiar is now made of gleaming mithral. Its Hardness increases from 10 to 15, and the lightweight metal allows it to move faster, increasing all speeds by 5 ft. per round.