You can probably find one at your nearest Lowes/HDepot. It will either be called a Flush Trim Bit or Laminate Trim Bit.
Specifically, it is a 2-Flute, Carbide Tipped, Flush Trim Bit with Ball Bearing. Look for a 1/4" diameter, cutting edge length between 1/2" to 1", 1/4" shank.