I'm looking for any item that will allow me to apply both metamagic feats (Still spell and Silent spell) to the same spell without raising the level of the spell slot it costs me.
I would have expected to be able to combine them in a rod at a cost of 9000gp for the lesser version, the same as Burning which has the same level modifier, but I cannot find such an item in the PRD, nor do I see rules for the creation of custom metamagic rods.
Any item which grants these would be acceptable to me. Limited uses per day or requiring me to already possess the feats would not be a problem.
Best Answer
Unless I'm misreading the description, I think the item you're looking for is the Caster's Tattoo.
Its only once per day, but nothing stops you from getting multiples if you're dedicated to having this capability.