$string =~ m[
	,           # a comma
	\s+         # followed by at least one space
	(           # capture
	      \d+   # one or more digits
	)
];

##</code><code>##

#! 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{
	# Strip the first five characters that we added earlier.
	substr $_, 5;
	
} sort { 
	# make the sort descending
	$b cmp $a 
	
} map {
	# print out the modified record to show what sprintf is doing
	print "before sort: '$_'";
	$_;
	
} map {
	
	## try the regex and die displaying 
	## the failing record if it doesn't match
	die "Regex did not match: '$_'" unless m[,\s+(\d+)];
	
	# It matched, so $1 contains the value to prepend.
	# pad to width 5.
	# use a bigger value here and above in the substr 
	# if your numbers can be bigger than 99999.
	sprintf '%05d%s', $1, $_;
	
} @array;

print $/;
print for @sorted;
__END__
P:\test>test2
before sort: '00002Item1 - 2 foo, 2 bar'
before sort: '00001Item2 - 0 foo, 1 bar'
before sort: '00003Item3 - 1 foo, 3 bar'
before sort: '00002Item4 - 1 foo, 2 bar'


Item3 - 1 foo, 3 bar
Item4 - 1 foo, 2 bar
Item1 - 2 foo, 2 bar
Item2 - 0 foo, 1 bar