A GRT will do it.

#! perl -slw
use strict;

my @array = split '\n', <<'EOA'; 
Item1 - 2 foo, 2 bar
Item2 - 0 foo, 1 bar
Item3 - 1 foo, 3 bar
Item4 - 1 foo, 2 bar
EOA

my @sorted = map{
    substr $_, 5;
} sort map{
    sprintf '%05d%s', 
        $_ =~ m[,\s+(\d+)], $_;
} @array;

print for @sorted;
__END__
Item2 - 0 foo, 1 bar
Item1 - 2 foo, 2 bar
Item4 - 1 foo, 2 bar
Item3 - 1 foo, 3 bar
[download]

Update: Limbic~Region pointed out that you wanted descending not ascending. so substitute sort { $b cmp $a } for  sort or use reverse on the results.