I believe there's a group that meets weekly on Weds. 9pm at Flamingo / Durango.
Check the Regional Thread at E90Post (see below)
As far as ///M specific groups not really sure. Although I did run into somebody with a Fire Orange M3 when I was in chinatown today. Had a nice short chat and was invited to come out to the weekly meet. From what he said there's around 5 - 6 ///M's that show up.