Whenever you want to manipulate listbox data, it's probably easiest to use the -listvariable option to store the tied array, then just manipulate the array( add to, then sort the array?). This should show you the idea:

#!/usr/bin/perl -w
use strict;
use Tk;

my $mw = Tk::MainWindow->new( -title => 'Listbox' );

my @array = ('A'..'Z');

my $lb = $mw->Scrolled('Listbox',
             -listvariable => \@array,
             )->pack();


my $b  = $mw->Button(
    -text    => 'Delete B',
    -command => sub{ del_it('B') },
)->pack();

MainLoop;

sub del_it {
    my $remove = shift;
    @array = grep { $_ ne 'B' } @array;
}
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