...
my %dirs;
find(\&dir_names, $wellpath);
print "$_\n" for sort keys %dirs;

sub dir_names
{
    # skip over everything that is not a directory
    return unless -d $File::Find::name;

    # skip over directories that don't match required pattern
    return unless $File::Find::dir =~ /[IPD]\d{8}$/;

    $dirs{$File::Find::dir} = 1;
}