Have a look at the SideFinder page at http://www.morrisdancing.org/finder/sfcgi.html, part of the combined morris pages.

Enter your postcode and you'll get a list of sides around that area.

I presume that the data set is based on the membership lists of the Federation, Open, and Ring, but the great majority of active sides are in one or other of those groups - it certainly looked comprehensive enough for my neck of the woods.