As everyone else stated, there called Torx bits. You can usually get a complete set for around $24 but if you buy them one at a time, they will cost you around $8. The Torx bits for seatbelts are actually called Torx Plus but a standard Torx bit will work, just be carefull not to round the edges off the bolt. It will most likely be a T-55 Torx Plus. The Torx Plus bits are just a tad bigger and have rounded edges instead of the squared off edges that a standard Torx bit has.
Yes, most any auto parts store or Sears will have the standard Torx bits. You will most likely have to find a Snap on truck to get the Torx Plus bits.