Lots of cleats available at Nashbar, and other online sources.
Your LBS might be able to tell you if they are able to order the parts.
I'm seeing the X-series on the Speedplay website.
Everything on the Speedplay site indicates no cross compatibility of the cleats with the X series. Looking at them, your cleats seem to have a round bar holding them in place, while the other series have more of a flat bar with a pin to hold them in place. So, I'm not surprised there might be compatibility issues.
It might not hurt to order a couple of pairs of cleats, just in case.