What you have there is called a double square screw or bolt head, and takes a special double square bit. There's really nothing else that will fit that particular head.
I worked at Lowes, and did carry 2 sizes of those bits in the hardware dept, Used to drive some specialty exterior screws we carried, made by FastenMaster.
Not there anymore, and I don't remember the sizes they were available in.
Check Ace or TrueValue--they may carry them.