Campagnolo spokes can fit other models, years and positions, please refer to the Campagnolo Technical documentation with the reference number from your rim to find the correct spokes for your wheels.
Please visit: http://www.campagnolo.com/UK/en/Support/download?td=3
for the technical documentation for every model of wheel by year.
Spokes are generally sold either as individuals or in mini spoke kits that contain 2 of each length.