This seems to do what you want without too much thrashing around. It should cope with overlapping sets (5 or more consecutive numbers) although I haven't tested that.

use strict;
use warnings;

use Data::Dumper;

my @a1 = ( 100, 204, 312 );
my @a2 = ( 102, 313, 409 );
my @a3 = ( 205, 206, 315 );
my @a4 = ( 207, 210, 314 );

## Two contiguous sequences of 4 values: 204 .. 207 & 312 .. 315

my $arrayNo = -1;

my @ints =
   sort {$a->[0] <=> $b->[0]}
   map
   {
       my $raOrig = $_;
       my @items = ();
       push @items,
          [$raOrig->[0]->[$_], qq{$raOrig->[1]:$_}]
          for 0 .. $#{$raOrig->[0]};
       @items;
   }
   map
   {
       $arrayNo ++;
       [$_, $arrayNo]
   }
   \@a1, \@a2, \@a3, \@a4;

my @sets;
for my $window (0 .. $#ints - 3)
{
    push @sets, [@ints[$window .. $window + 3]]
       if $ints[$window]->[0] == $ints[$window + 3]->[0] - 3;
}

print Dumper \@sets;
[download]

The Dumper output is

$VAR1 = [
          [
            [
              204,
              '0:1'
            ],
            [
              205,
              '2:0'
            ],
            [
              206,
              '2:1'
            ],
            [
              207,
              '3:0'
            ]
          ],
          [
            [
              312,
              '0:2'
            ],
            [
              313,
              '1:1'
            ],
            [
              314,
              '3:2'
            ],
            [
              315,
              '2:2'
            ]
          ]
        ];
[download]

I hope this is of use.

Cheers,

JohnGG

Update: Removed superfluous variable $elemNo left over from development