I tried do something locally this winter, response was pretty lacklustre. Of the 17 people that I know of that play or have played WM in the north east, I head back from four (the guys that I play with most often). I'm trying again for July, just going to set the date and see who comes out. In terms of something outside the north east, I thinking seven would be willing to do something within driving distance. Maybe a PA con? After that, four of us are willing to fly some place for a weekend of gaming (Adepticon).
As to other groups, I know there's a few guys in PA, FL, TX and CO from talking to them on this forum and/or shipping them minis.
