While not free (the full version), Sound on Sound magazine (October 2004 / June 2005) wrote a definitive technical review of the M1 plugin.
Simply load these samples into a free sampler like Grace or TX16Wx to recreate the M1 experience within your DAW. Key Features to Look For korg m1 plugin free
Many producers prefer samples over plugins because they are "CPU-light." Legowelt Korg M1 Pack: While not free (the full version), Sound on