With metrics, you will not get National Coarse/National Fine thread (or NC/ NF) - that's imperial thread. Metrics are denoted in the size and measured thread pitch in mm ie M8*1.0, M10*1.25, M12*1.75 etc. as well as the threaded shaft length.
Sabre industrial in Tilbury has a good selection of metrics and they like to deal in bulk, so maybe take in a few of your M6's m8's and m10s (that's most of what you'll need) and get them to measure the pitch for you and set you up with a few mixed boxes.