#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %h1 = ( a => 1,
	   b => 2,
	   c => 3, );

my %h2 = ( a => 4,
	   b => 5,
	   d => 10, );

my %h3 = ( x => 20,
	   p => 15,
	   b => 6,
	   a => 12, );

my %HoA;
foreach my $key (keys %h1) {
    push(@{$HoA{$key}}, $h1{$key}, $h2{$key}, $h3{$key})
	if exists $h2{$key} and exists $h3{$key};
}
print Dumper \%HoA;

__END__

$ perl test.pl
$VAR1 = {
          'b' => [
                   2,
                   5,
                   6
                 ],
          'a' => [
                   1,
                   4,
                   12
                 ]
        };