I believe it is currently wired with a 14 gauge cord. If you inspect the old cable you should see it imprinted into the side. It would say either 12/3 AWG or 14/3 AWG. The 3 indicates the number of conductors, in this case (for 110v), positive (black), negative or neutral (white) and ground (green). Simply put, the gauge is the diameter of the wire, the lower the number the greater the diameter and the greater the capacity. 12 gauge carries more amps than 14 gauge. If the cord is currently 14 gauge then you could replace it with either 14 or 12. If it is 12, replace it with 12. There is one other consideration. If you are using the saw in your garage, with an outlet near by, then no worries. If you are planning to haul it to a job site or outbuilding and power it with an extension cord, then I would suggest 12 gauge. It may not be necessary but it does help to protect the motor. Using an undersized cord will burn out a saw motor before it's time.
As for where to buy, any hardware store, Home Depot, Lowes, etc. will carry it. You may also want to buy a new plug. The one you have there is kind of a pain to wire. The final variable is the thickness of the outer jacket of the cord. Again, unless you are dragging it around a lot, any will do.
So figure out the gauge, the length you need / desire, and hit the store. They should be able to point you in the right direction. As an option to buying actual cord, you could also buy an appropriate gauge extension cord and cut the female end off.
