Look around under/inside the cabinets and find a junction box. If it doesn't need its own separate circuit, then you can open the junction box and make your connection there. Make sure you use a strain relief on the new wire where it goes into the junction box through one of the knockouts. 12/2 romex with ground is good for a 20amp circuit. I think NEC allows up to 12 or 13 outlets on a 20amp circuit. Just make sure that you get the right sized outlet too... if you have a 20amp circuit, get a 20 amp outlet.