I have never seen an MLS receiver or an airport equipped with MLS.
I dug up some old BA Maintenance Manuals and Schematics which showed MLS circuit breakers, antennas, antenna switching relays and ILS/MLS Switching Relays, but the receivers are marked as "provisional". When I first saw the MLS antennas underneath the nose on BA (many moons ago), it took me a while to figure out what they were.
Do the MMRs have optional modules for MLS?