This brute force symmetry analyzer used to be available at
S. Patchkovskii's website http://www.cobalt.chem.ucalgary.ca/ps/symmetry/ which seems to be down.
Here you can find a copy of the file and a makefile with an example that you can run by typing make example.
The example will download a 13 atom Icosahedral Lennard-Jones cluster from the Cambridge Cluster Database, will format the file according to the input that symmetry.out takes and will run it to obtain the symmetry group of the cluster.