Help finding a second hand air compressor

[CliffyG]

I'm trying to replace the faulty air conditioning compressor in my wife's 06 Mazda 3 Sport and am a little confused. The model number on the existing unit is H12A0BW4JZ but this doesn't seem to match any of the ones I can find on ebay for that car. I'm assuming there is a mix of models for the mazda 3 but cant find any info on what ones are compatible with what. Bit of a long shot but was wondering if anyone on here knows.