my @dates = grep /$date/, @{ $countries{$cntry_of_issue} };

##</code><code>##

use warnings;
use strict;
use Data::Dumper;

my %countries;
while (<DATA>) {
        chomp;
        next if /^\s*$/ || /^\#/;
        my $aref = [split /,/, $_];
        push( @{$countries{$aref->[2]}}, $aref->[5]);
}

my $date = 20100101;
my $cntry_of_issue = 'CH';
my @dates = grep /$date/, @{ $countries{$cntry_of_issue} };
print Dumper(\@dates);

__DATA__
978,XBRN,CH,Berne Stock Exchange,2010,20100101
978,XBRN,CH,Berne Stock Exchange,2010,20100102
978,XBRN,CH,Berne Stock Exchange,2010,20100321
978,XBRN,CH,Berne Stock Exchange,2010,20100324

##</code><code>##

$VAR1 = [
          '20100101'
        ];