The Ritchey pads may work, but they are designed for "linear pull" otherwise known as v-brakes. There is a chance that they will be too thick to fit properly on an old center pull brakeset. The two I suggested are designed for caliper brakes, and the Aztecs are even the same blocky squared off shape as the original Dia Compe pads, which (as brokenrobot said) may be available cheaply from your LBS.