Have you tried digikey? They don't seem to have the exact part number you are seeking. But they do have MX1A-E1NW which is a similar part but without the internal diode. Not sure what impact this will have with the Kinesis keyboard however.
Interestingly enough, the part number is not listed in the MX series datasheet. What is the PCB layout like, would you be able to splice in SMD diodes where they are needed :)